Birthday Boy

Excretive Magic. Whenever a spell slot is expended within 10 feet of the homunculus, its hit points increase by an amount equal to the spell's level. The homunculus must spend a number of hit points to use its special abilities. 

Might of the Master. The homunculus uses its master's spellcasting ability modifier, spell attack modifier, and spell save DC when casting spells.  

(Require Your Bonus Action)

Acidic Spittle (Costs 1 hp). The homunculus hurls a bubble of acid. Choose one or two creatures it can see within 30 feet. If you choose two, they must be within 5 feet of each other. A target must succeed on a Dexterity saving throw or take 1d6 acid damage.

Alchemical Salve (Costs 2 hp). A creature the homunculus touches regains a number of hit points equal to 1d8 + your spellcasting ability modifier. This salve has no effect on undead or constructs.

Projectile Vomit (Costs 3 hp). The homunculus vomits an undulating, warbling mass of chaotic energy at one creature within 60 feet. Make a ranged spell attack against the target. On a hit, the target takes 2d8 + 1d6 damage. Choose one of the d8s. The number rolled on that die determines the attack’s damage type (1=acid, 2=cold, 3=fire, 4=force, 5=lightning, 6=poison, 7=psychic, 8=thunder).

If you roll the same number on both d8s, the chaotic energy splashes from the target to a different creature of your choice within 30 feet of it. Make a new attack roll against the new target, and make a new damage roll, which could cause the chaotic energy to leap again. A creature can be targeted only once by each projectile vomit.