✨ Add final boss

contracts/Dungeon.sol

@@ -18,6 +18,7 @@ contract Dungeon {
     Spawner public $spawner;
     NPC public $storyTeller;
     NPC public $mathematican;
+    NPC public $finalBoss;
 
     mapping(bytes4 => bool) public $quests;
     uint256 private $traps;
@@ -60,6 +61,14 @@ contract Dungeon {
         _;
     }
 
+    modifier bossSpawned() {
+        require(
+            $quests[this.spawnFinalBoss.selector] == true,
+            "These functions cannot be called"
+        );
+        _;
+    }
+
     modifier lootGained() {
         require(
             $quests[this.lockedChest.selector] == true,
@@ -147,10 +156,15 @@ contract Dungeon {
     }
 
     // get 10000 tokens
-    function spawnFinalBoss() external altarFound cleanRoom lootGained challenger takeQuest {
-        NPC finalBoss = NPC(_spawn(keccak256("finalBoss"), type(FinalBoss).creationCode));
-        bytes memory result = finalBoss.interaction(abi.encodePacked(msg.sender));
-        _attempt(abi.decode(result, (bool)) == true, 10000, msg.sender, "What a legend!", "You have been defecated");
+    function spawnFinalBoss() external challenger altarFound cleanRoom lootGained takeQuest {
+        $finalBoss = NPC(_spawn(keccak256("finalBoss"), abi.encodePacked(type(FinalBoss).creationCode, abi.encode(msg.sender))));
+    }
+
+    function finalBoss() external bossSpawned takeQuest {
+        uint256 defeated;
+        address f = address($finalBoss);
+        assembly { defeated := extcodesize(f) }
+        _attempt(defeated == 0, 10000, msg.sender, "What a legend!", "You have been defecated");
     }
 
     // get something

contracts/FinalBoss.sol

@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: None
+
+pragma solidity =0.8.20;
+
+import "./NPC.sol";
+
+contract FinalBoss is NPC {
+    uint256 public $hp = 9;
+    bytes32 [] public lostSouls;
+
+    address $challenger;
+
+    constructor(address challenger) {
+        $challenger = challenger;
+    }
+
+    modifier onlyChallenger() {
+        require(msg.sender == $challenger, "You're not the challenger!");
+        _;
+    }
+
+    modifier vulnerable() {
+        require($hp == 1, "Still fresh.");
+        _;
+    }
+
+    function bestiary() external pure returns (string memory) {
+        return "Yuller - Dangerous robber of yul souls. He's trying to sell them in dark forests for imaginary prices.";
+    }
+
+    function interaction(bytes memory input) external override returns (bytes memory output) {
+        uint256 hp = abi.decode(input, (uint256));
+        require(hp >= 9, "Try to hurt me!");
+        $hp = hp;
+        return bytes(hex"dead");
+    }
+
+    function helpFromYulSouls() external onlyChallenger {
+        assembly {
+            let lives := sload($hp.slot)
+            let soulPower := sload(lostSouls.slot)
+            let soulEnergy := add(soulPower, 0x20)
+            let soulStrength := mul(soulEnergy, 0x02)
+            sstore(keccak256(lostSouls.slot, 0x20), soulStrength)
+            let soulLength := sload(lostSouls.slot)
+            let soulIndex := mod(keccak256(lostSouls.slot, 0x20), soulLength)
+            let helpfulSoul := sload(add(lostSouls.slot, soulIndex))
+            sstore(keccak256(lives, 0x20), helpfulSoul)
+        }
+    }
+
+    // rewrite to assembly
+    function addSouls(bytes32 soul) external onlyChallenger {
+        lostSouls.push(soul);
+    }
+
+    // rewrite to assembly
+    function replaceSouls(uint256 which, bytes32 soul) external onlyChallenger {
+        lostSouls[which] = soul;
+    }
+
+    function releaseSouls() public onlyChallenger {
+        assembly {
+            sstore(lostSouls.slot, sub(sload(lostSouls.slot), 1))
+        }
+    }
+
+    function catchSouls() public onlyChallenger {
+        assembly {
+            sstore(lostSouls.slot, add(sload(lostSouls.slot), 1))
+        }
+    }
+
+    function kill(address backpack) external override vulnerable onlyChallenger {
+        selfdestruct(payable(backpack));
+    }
+
+    function givelife(bytes memory lifeform) external override payable {
+        revert("Why should I do that?");
+    }
+}

contracts/NPC.sol

@@ -7,11 +7,11 @@ contract NPC {
         return bytes(hex"42");
     }
 
-    function kill(address backpack) external {
+    function kill(address backpack) external virtual {
         selfdestruct(payable(backpack));
     }
 
-    function givelife(bytes memory lifeform) external payable {
+    function givelife(bytes memory lifeform) external virtual payable {
         assembly {
             if iszero(create(0, add(lifeform, 32), mload(lifeform))) {
                 revert(0, 0)