Sylvester

It appears on round 300. It has 500,000 health, it cannot be hurt by towers (Towers will not attack it) and will be eaten by it. It will not go to the exit but to lose, you have got to lose all of your cash. Instead, to attack it, you have a gun that does 10,000, each shot costs 1,000 cash, you start with 10,000,000 cash. It will summon Z.O.M.G.s however that require only one hit and will not spawn any children. However, they do not give cash. It can also spawn B.F.B.s rarely that give 200,000 cash and require only one hit. At 100,000 damage taken, it will spawn an I.G.B.M that takes 1 hit to destroy but explodes once killed and does not give cash but gives 5,000 lives. At 250,000 damage taken, it will spawn an I.N.F.I.N.I.T.Y. with the speed of a B.F.B. and takes 10 hits to destroy and releases 4 B.L.I.T.Z.s.

Trivia

 * The BGM of the boss fight is an alien fight in Insaniquarium.
 * The reference is Insaniquarium.