I listen to the jokes, and then move on.
Floor 270 is a MATHS EXAM that you have to complete and get an A on or Omega Dungeon Guardians (1000000000000000000 HP, 1000000000000000000 damage, 1000000000000000000 defence and 99.999999999999999% DR, same AI as DG) will attack you when you leave the room. Or you can kill Omega Skeletron by cursing the old lady in the room. Omega Skeletron: Head has 1000000 health, does 250 (300 when spinning) contact damage, has 100 (10000 when spinning) defence and uses Head AI. Has 8 hands. Cannon hand: Has 3 cannons attached to it that work like the ones on Skeletron Prime, does no contact damage but cannonballs do 320 damage, has 10000 health and 50 defence. Laser hand: Alternates between firing red lasers like Skeletron Prime at same speed but 3 at a time, blue lasers in a barrage like Ocram on the 360 and PS3 and yellow lasers that continuously flre where the hand was aimed when starting the attack. Red lasers do 320 damage, blue lasers do 200 damage and yellow lasers do 150 damage. Has 10000 health and 50 defence. Bow hand: Works like Phantasm, shooting 4 arrows. Does no contact damage but arrows do 200 damage, has 10000 health and 50 defence. Sword hand: Swings about like crazy, doing 350 contact damage and having 10000 health and 50 defence.
Stinger hand: Hand that can shoot 4 stingers at once. It is also itself a big stinger. Shot stingers do 200 danage plus 25% change of poison and 8.33 percent chance of venom. Hand itself has 10000 health, 50 defence and does 300 contact damage with a 75% chance of poison and a 25% chance of venom. Bomber hand: drops bombs that destroy most tiles, do 1000 damage and have a radius of 13 blocks. Does this every 20 seconds, has no contact damage and has 10000 health and 50 defence.
Skeletron hand: Literally just a Skeletron except it doesn't anger during day. Prime hand: Literally just Skeletron Prime except it doesn't anger during day. Omega Skeletron also has minions not unlike The Hungries from the Wall of Flesh fight except they are skulls. 30 spawn with the boss, they have 1000 health each, detach from the boss after losing 500 health and use same AI.
EDIT: Omega Skeletron is also innume to damage over 1000 and explosions.