First boss 32 hp. 0 and 1 attack does 1 damage, 2 attack does 2 damage
Second boss 40 hp, 2 and 3 attack does 2 damage, 4 and 5 attack does 3 damage
Third boss 48 hp, 3 attack does 2 damage, 4 and 5 does 3 damage
Fourth boss 56 hp, 2 and 3 attack does 2 damage, 4 and 5 does 3 damage
Fifth boss 64 hp, 2 and 3 attack does 2 damage, 4 and 5 does 3 damage

Stomp starts at 3 and goes up by 1 per level

The damage numbers seem to be pretty static in the fact that 0-1 does 1 damage to all bosses, 2-3 does 2 damage to all bosses, and 4-5 does 3 damage to all bosses. Stomp is a static amount of damage as well and scales slightly better than melee damage, but has a very long animation making it not worth being used.