diff --git a/config/api_platform/resources.xml b/config/api_platform/resources.xml
index 023144a..9f3de08 100644
--- a/config/api_platform/resources.xml
+++ b/config/api_platform/resources.xml
@@ -143,14 +143,22 @@
 
 <resource class="App\Entity\TournamentRegistration">
     <operations>
-        <operation class="ApiPlatform\Metadata\Post" />
+        <operation class="ApiPlatform\Metadata\Post"  processor="App\State\TournamentRegistrationStateProcessor"/>
     </operations>
 </resource>
 
 <resource class="App\Entity\Fight">
     <operations>
         <operation class="ApiPlatform\Metadata\Get" />
-        <operation class="ApiPlatform\Metadata\GetCollection" controller="App\Controller\GetTournamentFights" uriTemplate="tournament/{tournamentId}/fights" description="Receives the fights from a tournament."/>
+        <operation class="ApiPlatform\Metadata\GetCollection" controller="App\Controller\GetTournamentFights" uriTemplate="tournaments/{tournamentId}/fights" description="Receives the fights from a tournament.">
+            <uriVariables><uriVariable parameterName="tournamentId" fromClass="App\Entity\Tournament"></uriVariable></uriVariables>
+        </operation>
+        <operation class="ApiPlatform\Metadata\GetCollection" controller="App\Controller\GetTournamentFights" uriTemplate="tournaments/{tournamentId}/characters/{characterId}/fights" description="Receives the fights from a tournament for a given character.">
+            <uriVariables>
+                <uriVariable parameterName="tournamentId" fromClass="App\Entity\Tournament"></uriVariable>
+                <uriVariable parameterName="characterId" fromClass="App\Entity\Character"></uriVariable>
+            </uriVariables>
+        </operation>
     </operations>
 </resource>
 
diff --git a/src/Controller/GetTournamentFights.php b/src/Controller/GetTournamentFights.php
index 9d3d0a5..af55de5 100644
--- a/src/Controller/GetTournamentFights.php
+++ b/src/Controller/GetTournamentFights.php
@@ -13,8 +13,6 @@ class GetTournamentFights
     {
         return $em->getRepository(Fight::class)->findBy([
             'tournament' => $tournamentId
-        ], [
-            'startDate' => 'ASC'
         ]);
     }
 }
diff --git a/src/Entity/Character.php b/src/Entity/Character.php
index 38443b4..b1bae6e 100644
--- a/src/Entity/Character.php
+++ b/src/Entity/Character.php
@@ -167,17 +167,19 @@ class Character extends Thing
     }
 
     /**
-     *
-     * @return Technique[]
+     * @return Collection<int, Technique>
      */
-    public function getTechniques(): mixed
+    public function getTechniques(): Collection
     {
-        return $this->techniques->getValues();
+        return $this->techniques;
     }
 
     public function addTechnique(Technique $technique): static
     {
-        $this->techniques[] = $technique;
+        if (!$this->techniques->contains($technique)) {
+            $this->techniques->add($technique);
+        }
+
         return $this;
     }
 
diff --git a/src/Entity/Dojo.php b/src/Entity/Dojo.php
index 1323ff4..c0c4512 100644
--- a/src/Entity/Dojo.php
+++ b/src/Entity/Dojo.php
@@ -62,7 +62,6 @@ class Dojo extends Thing
     }
 
     /**
-     *
      * @return Collection<int, Character>
      */
     public function getMembers(): Collection
@@ -72,7 +71,7 @@ class Dojo extends Thing
 
     public function addMember(Character $member): static
     {
-        if (! $this->members->contains($member)) {
+        if (!$this->members->contains($member)) {
             $this->members->add($member);
             $member->setDojo($this);
         }
diff --git a/src/Entity/Fight.php b/src/Entity/Fight.php
index bf6d0c8..0c0e11b 100644
--- a/src/Entity/Fight.php
+++ b/src/Entity/Fight.php
@@ -21,7 +21,6 @@ class Fight extends Thing
     private array $events = [];
 
     #[ORM\ManyToOne]
-    #[ORM\JoinColumn(nullable: false)]
     private ?Character $winner = null;
 
     #[ORM\ManyToOne(inversedBy: 'fights')]
diff --git a/src/Entity/Tournament.php b/src/Entity/Tournament.php
index c616d89..170c88d 100644
--- a/src/Entity/Tournament.php
+++ b/src/Entity/Tournament.php
@@ -23,6 +23,9 @@ class Tournament extends Thing
     #[ORM\OneToMany(mappedBy: 'tournament', targetEntity: Fight::class)]
     private Collection $fights;
 
+    #[ORM\ManyToOne]
+    private ?Character $winner = null;
+
     public function __construct()
     {
         $this->characters = new ArrayCollection();
@@ -108,4 +111,16 @@ class Tournament extends Thing
 
         return $this;
     }
+
+    public function getWinner(): ?Character
+    {
+        return $this->winner;
+    }
+
+    public function setWinner(?Character $winner): static
+    {
+        $this->winner = $winner;
+
+        return $this;
+    }
 }
diff --git a/src/Entity/TournamentRegistration.php b/src/Entity/TournamentRegistration.php
index 4a7e731..193fee3 100644
--- a/src/Entity/TournamentRegistration.php
+++ b/src/Entity/TournamentRegistration.php
@@ -1,11 +1,15 @@
 <?php
 namespace App\Entity;
 
+use App\Validator\CharacterOwned;
+use App\Validator\StartDateInFuture;
+
 class TournamentRegistration
 {
 
+    #[StartDateInFuture()]
     public Tournament $tournament;
 
+    #[CharacterOwned()]
     public Character $character;
 }
-
diff --git a/src/State/TournamentRegistrationStateProcessor.php b/src/State/TournamentRegistrationStateProcessor.php
new file mode 100644
index 0000000..a921c30
--- /dev/null
+++ b/src/State/TournamentRegistrationStateProcessor.php
@@ -0,0 +1,41 @@
+<?php
+namespace App\State;
+
+use ApiPlatform\Metadata\Operation;
+use ApiPlatform\State\ProcessorInterface;
+use App\Entity\TournamentRegistration;
+use Doctrine\ORM\EntityManagerInterface;
+use Symfony\Component\DependencyInjection\Attribute\Autowire;
+use Symfony\Component\HttpFoundation\Exception\BadRequestException;
+
+class TournamentRegistrationStateProcessor implements ProcessorInterface
+{
+
+    public function __construct(
+        #[Autowire(service: 'api_platform.doctrine.orm.state.persist_processor')] private ProcessorInterface $persistProcessor,
+        private EntityManagerInterface $em)
+    {}
+
+    public function process(mixed $data, Operation $operation, array $uriVariables = [], array $context = []): TournamentRegistration
+    {
+        $this->updateData($data);
+        $result = $this->persistProcessor->process($data, $operation, $uriVariables, $context);
+
+        return $result;
+    }
+
+    private function updateData(TournamentRegistration $registration): void
+    {
+        $tournament = $registration->tournament;
+        $character = $registration->character;
+
+        if ($tournament->getCharacters()->contains($character)) {
+            throw new BadRequestException("Character is already registered!");
+        }
+
+        $registration->tournament->addCharacter($registration->character);
+        $this->em->persist($registration->tournament);
+        $this->em->persist($registration->character);
+        $this->em->flush();
+    }
+}
diff --git a/src/Validator/CharacterOwned.php b/src/Validator/CharacterOwned.php
new file mode 100644
index 0000000..2d5c11b
--- /dev/null
+++ b/src/Validator/CharacterOwned.php
@@ -0,0 +1,12 @@
+<?php
+namespace App\Validator;
+
+use Symfony\Component\Validator\Constraint;
+
+#[\Attribute(\Attribute::TARGET_PROPERTY | \Attribute::IS_REPEATABLE)]
+class CharacterOwned extends Constraint
+{
+
+    public string $invalidOwnerMessage = 'Character is not from the dojo of the current user';
+}
+
diff --git a/src/Validator/CharacterOwnedValidator.php b/src/Validator/CharacterOwnedValidator.php
new file mode 100644
index 0000000..2ddd1d5
--- /dev/null
+++ b/src/Validator/CharacterOwnedValidator.php
@@ -0,0 +1,33 @@
+<?php
+namespace App\Validator;
+
+use App\Entity\Character;
+use Symfony\Bundle\SecurityBundle\Security;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedValueException;
+
+class CharacterOwnedValidator extends ConstraintValidator
+{
+
+    public function __construct(private Security $security)
+    {}
+
+    public function validate($character, Constraint $constraint): void
+    {
+        if (! $character instanceof Character) {
+            throw new UnexpectedValueException($character, Character::class);
+        }
+
+        if (! $constraint instanceof CharacterOwned) {
+            throw new UnexpectedValueException($constraint, CharacterOwned::class);
+        }
+
+        if ($character->getDojo()
+            ->getOwner()
+            ->getId() != $this->security->getUser()->getUserIdentifier()) {
+            $this->context->buildViolation($constraint->invalidOwnerMessage)->addViolation();
+        }
+    }
+}
+
diff --git a/src/Validator/StartDateInFuture.php b/src/Validator/StartDateInFuture.php
new file mode 100644
index 0000000..7e8728f
--- /dev/null
+++ b/src/Validator/StartDateInFuture.php
@@ -0,0 +1,12 @@
+<?php
+namespace App\Validator;
+
+use Symfony\Component\Validator\Constraint;
+
+#[\Attribute(\Attribute::TARGET_PROPERTY | \Attribute::IS_REPEATABLE)]
+class StartDateInFuture extends Constraint
+{
+
+    public string $invalidStartDateMessage = 'Start date has already passed';
+}
+
diff --git a/src/Validator/StartDateInFutureValidator.php b/src/Validator/StartDateInFutureValidator.php
new file mode 100644
index 0000000..8ee3be9
--- /dev/null
+++ b/src/Validator/StartDateInFutureValidator.php
@@ -0,0 +1,27 @@
+<?php
+namespace App\Validator;
+
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+use Symfony\Component\Validator\Exception\UnexpectedValueException;
+use DateTimeImmutable;
+use DateTimeZone;
+
+class StartDateInFutureValidator extends ConstraintValidator
+{
+
+    public function __construct()
+    {}
+
+    public function validate(mixed $entity, Constraint $constraint): void
+    {
+        if (! $constraint instanceof StartDateInFuture) {
+            throw new UnexpectedValueException($constraint, CharacterStats::class);
+        }
+
+        if ($entity->getStartDate() < new DateTimeImmutable("now", new DateTimeZone("UTC"))) {
+            $this->context->buildViolation($constraint->invalidStartDateMessage)->addViolation();
+        }
+    }
+}
+
diff --git a/tests/AbstractTest.php b/tests/AbstractTest.php
index bb5f96b..7ce59bd 100644
--- a/tests/AbstractTest.php
+++ b/tests/AbstractTest.php
@@ -4,6 +4,7 @@ namespace App\Tests;
 use ApiPlatform\Symfony\Bundle\Test\ApiTestCase;
 use ApiPlatform\Symfony\Bundle\Test\Client;
 use App\Entity\Thing;
+use Doctrine\ORM\EntityManagerInterface;
 use Zenstruck\Foundry\Proxy;
 use Zenstruck\Foundry\Test\Factories;
 use Zenstruck\Foundry\Test\ResetDatabase;
@@ -48,5 +49,10 @@ abstract class AbstractTest extends ApiTestCase
         }
         return $this->getIriFromResource($thing);
     }
+
+    protected function getEntityManager(): EntityManagerInterface
+    {
+        return static::$kernel->getContainer()->get('doctrine.orm.entity_manager');
+    }
 }
 
diff --git a/tests/TournamentTest.php b/tests/TournamentTest.php
index 54d0b72..37b2ec8 100644
--- a/tests/TournamentTest.php
+++ b/tests/TournamentTest.php
@@ -1,29 +1,53 @@
 <?php
 namespace App\Tests;
 
+use App\Entity\Character;
+use App\Entity\Tournament;
+use App\Entity\User;
 use App\Factory\CharacterFactory;
 use App\Factory\DojoFactory;
+use App\Factory\FightFactory;
 use App\Factory\TournamentFactory;
 use App\Factory\UserFactory;
+use Zenstruck\Foundry\Proxy;
+use DateTimeImmutable;
+use DateTimeZone;
 
+// @note No need to create tournaments via API Endpoint ... will be done in cronjob
 class TournamentTest extends AbstractTest
 {
 
-    // No need to create tournaments via API Endpoint ... will be done in cronjob
-    public function testRegisterCharacter(): void
+    private function createTournament(string $offset, array $characters = array()): Tournament|Proxy
     {
-        $tournament = TournamentFactory::createOne();
+        $tournamentStartDate = new DateTimeImmutable("now", new DateTimeZone("UTC"));
+        $tournamentStartDate = $tournamentStartDate->sub(\DateInterval::createFromDateString($offset));
 
+        return TournamentFactory::createOne([
+            'startDate' => $tournamentStartDate,
+            'characters' => $characters
+        ]);
+    }
+
+    private function createCharacter(User|Proxy $user): Character|Proxy
+    {
         $dojo = DojoFactory::createOne([
-            'owner' => UserFactory::createOne()
+            'owner' => $user
         ]);
 
         $character = CharacterFactory::createOne([
             'dojo' => $dojo
         ]);
 
-        $response = static::createClientWithToken($dojo->getOwner()->authName)->request('POST',
-            '/api/tournament_registrations',
+        return $character;
+    }
+
+    public function testRegisterCharacter(): void
+    {
+        $tournament = $this->createTournament("-5 min");
+        $user = UserFactory::createOne();
+        $character = $this->createCharacter($user);
+
+        static::createClientWithToken($user->authName)->request('POST', '/api/tournament_registrations',
             [
                 'json' => [
                     'tournament' => $this->getIri($tournament),
@@ -32,40 +56,142 @@ class TournamentTest extends AbstractTest
             ]);
 
         $this->assertResponseStatusCodeSame(201);
+    }
+
+    public function testRegisterCharacterDifferentUser(): void
+    {
+        $tournament = $this->createTournament("-5 min");
+        $characterOwner = UserFactory::createOne();
+        $character = $this->createCharacter($characterOwner);
+        $user = UserFactory::createOne();
 
-        $this->assertArrayHasKey('id', $response->toArray());
+        static::createClientWithToken($user->authName)->request('POST', '/api/tournament_registrations',
+            [
+                'json' => [
+                    'tournament' => $this->getIri($tournament),
+                    'character' => $this->getIri($character)
+                ]
+            ]);
+
+        $this->assertResponseStatusCodeSame(422);
+    }
+
+    public function testRegisterCharacterOnPastTournament(): void
+    {
+        $tournament = $this->createTournament("5 min");
+        $user = UserFactory::createOne();
+        $character = $this->createCharacter($user);
+
+        static::createClientWithToken($user->authName)->request('POST', '/api/tournament_registrations',
+            [
+                'json' => [
+                    'tournament' => $this->getIri($tournament),
+                    'character' => $this->getIri($character)
+                ]
+            ]);
+
+        $this->assertResponseStatusCodeSame(422);
     }
 
     public function testRegisterCharacterNotPossibleTwice(): void
-    {}
+    {
+        $tournament = $this->createTournament("-5 min");
+        $user = UserFactory::createOne();
+        $character = $this->createCharacter($user);
 
-    public function testRegisterCharacterOnPastTournament(): void
-    {}
+        static::createClientWithToken($user->authName)->request('POST', '/api/tournament_registrations',
+            [
+                'json' => [
+                    'tournament' => $this->getIri($tournament),
+                    'character' => $this->getIri($character)
+                ]
+            ]);
+
+        static::createClientWithToken($user->authName)->request('POST', '/api/tournament_registrations',
+            [
+                'json' => [
+                    'tournament' => $this->getIri($tournament),
+                    'character' => $this->getIri($character)
+                ]
+            ]);
+
+        $this->assertEquals(1,
+            $this->getEntityManager()
+                ->find(Tournament::class, $tournament->getId())
+                ->getCharacters()
+                ->count());
+        $this->assertResponseStatusCodeSame(400);
+    }
 
     public function testShowRegisteredCharacters(): void
-    {}
+    {
+        $tournament = $this->createTournament("-5 min", CharacterFactory::createMany(4));
+
+        $response = static::createClientWithToken()->request('GET', $this->getIri($tournament));
+        $this->assertResponseStatusCodeSame(200);
+        $this->assertCount(4, $response->toArray()['characters']);
+    }
 
     public function testListTournaments(): void
-    {}
+    {
+        TournamentFactory::createMany(5);
+        $response = static::createClientWithToken()->request('GET', '/api/tournaments');
+        $this->assertResponseStatusCodeSame(200);
+        $this->assertCount(5, $response->toArray());
+    }
 
     /**
      * Status is ...
      * meta data like when it is starting, name, "location", Winner (nullable), etc.
      */
     public function testTournamentStatus(): void
-    {}
+    {
+        $tournament = TournamentFactory::createOne([
+            'winner' => CharacterFactory::createOne()
+        ]);
+        $response = static::createClientWithToken()->request('GET', $this->getIri($tournament));
+        $this->assertResponseStatusCodeSame(200);
+
+        $arrayResponse = $response->toArray();
+        $this->assertArrayHasKey('winner', $arrayResponse);
+    }
 
-    // /api/tournament/{id}/fights
-    // readableLink: true -> participant ids and winner
     public function testTournamentFights(): void
-    {}
+    {
+        $tournament = TournamentFactory::createOne([
+            'fights' => FightFactory::createMany(16)
+        ]);
+
+        $response = static::createClientWithToken()->request('GET', $this->getIri($tournament) . '/fights');
+        $this->assertResponseStatusCodeSame(200);
+        $this->assertCount(16, $response->toArray());
+    }
 
-    // /api/tournament/{id}/character/{id}/fights
     public function testTournamentFightsForCharacter(): void
-    {}
+    {
+        $characters = CharacterFactory::createMany(16);
+        $tournament = TournamentFactory::createOne([
+            'characters' => $characters
+        ]);
 
-    // /api/tournament/{id}/ranking
-    public function testTournamentRanking(): void
-    {}
+        $winner = $characters[0];
+        for ($i = 1; $i < count($characters); ++ $i) {
+            $tournament->addFight(
+                FightFactory::createOne([
+                    'winner' => $winner,
+                    'characters' => array(
+                        $winner,
+                        $characters[$i]
+                    )
+                ])->object());
+        }
+        $tournament->save();
+
+        $response = static::createClientWithToken()->request('GET',
+            $this->getIri($tournament) . '/characters/' . $winner->getId()
+                ->toBase32() . '/fights');
+
+        $this->assertCount(15, $response->toArray());
+    }
 }