Please update the game with the following improvements and balance changes. Implement these modifications carefully, ensuring all existing core mechanics remain intact unless specified.

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### 1. SCORE AND CURRENCY SEPARATION
* **Fix:** Disconnect “Points” (Score) and “Money” (Coins/Currency) into two completely independent variables.
* *Current Bug:* Spending money currently reduces the player’s score.
* *Expected Behavior:* Spending money should ONLY decrease the money variable. The player’s score should never decrease when a purchase is made.

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### 2. ENEMY MODIFICATIONS & NEW BOSS

#### Enemy: Possessed Shark (Squalo Posseduto)
* **HP:** 15
* **Weapon/Damage:** Worn Scythe (Falce Logora) – Deals 6 damage on hit.
* **Behavior/Speed:** Ultra-fast; performs sudden, unpredictable dashes toward the player.
* **Spawn Rate:** Low (rare enemy).
* **Reward:** Gives +5 Money when defeated.

#### Final Boss: Giant Leviathan (Leviatano Gigante)
* **HP:** 190
* **Behavior/Speed:** Extremely fast movement.
* **Spawn Rate:** Only 1 spawns (Final Boss).
* **Attacks:**
* Deals 6 damage instantly upon colliding with/touching the player.
* Shoots projectiles at a rate of 2 shots per second.
* **Immunities:** Completely immune to the “Black Hole Gun” (Spara Buchi Neri).

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### 3. WAVE ADJUSTMENTS & NEW HAZARDS

#### Wave 4 & Wave 5 Additions: Toxic Seaweed (Alghe Tossiche)
* **HP:** 100
* **Movement:** Stationary (does not move).
* **Spawn Rate:** Medium density during Waves 4 and 5.
* **Attacks:**
* Shoots 2 very large projectiles at a time.
* Deals Poison Damage: Slowly ticks away health (-1 HP per tick/second) upon contact or projectile hit.

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### 4. ENVIRONMENT & BACKGROUND ELEMENTS (Visuals & Hazards)
Add the following graphical and interactive elements to the background/map:
* **Ghost Ship (Vascello Fantasma):** Decorative background element.
* **Rocks (Rocce):** Decorative obstacles.
* **Swimming Humans (Umani che nuotano):** Ambient background elements.
* **Whirlpool/Vortex (Vortice):** Interactive hazard. If the player passes over it, it drains 1 HP per second.

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### 5. NEW COLLECTIBLE ITEMS
* **Heart Seaweed (Alghe Cuore):** Useful items spawned in the water.
* **Effect:** Restores +1 HP to the player upon collection.
* **Spawn Rate:** Exactly 5 Heart Seaweeds must spawn during each wave.