Here are the buttons:

Zombie - Summons a couple zombies with a zombie villager as a boss.

Skeleton - Summons a few skeletons with bows and a wither skeleton boss.

Slime - Summons a ton of slimes and a magma cube boss.

Blaze - Summons some Zombie Pigmen, some Blazes and a Ghast for a boss.

Guardian - Summons a tons of Guardians and an Elder boss.

Herobrine - Summons a whole ton of different mobs, ranging from easy to impossible. Creepers with speed and quick fuses. Slowly approaching Flames who cannot be knocked back and look like just a column of flame. These Flames will continues spawning to infinity until you step on a Bedrock block. And, of course, as a boss we have HEROBRINE. He can't be beat (Or can he?). You might as well just give up. Right?

Here are the blocks:

DIAMOND - Heavy: Diamond armor and sword, permanent Slowness II effect.

GOLD - Archer: Golden armor and bow. Different arrows with different effects.

IRON - Soldier: Iron sword and armor. Permanent speed and jump boost.

COAL - Ninja: Black boots and golden sword with enchantments. Fast speed and ender pearls to teleport. Hold the nether star to turn invisible!

SEA LANTERN - Deity: Nothing but a single bow and arrow. Invulnerable to all mobs. Bow has insanely powerful enchantments.

BEDROCK - Kill all mobs. Stops the infinite wave. Will not kill subsequent mobs such as magma cube babies.