The Underground Sea is a versatile Land card illustrated with a mystical seascape that can be used as either an island or a swamp, depending on the players current needs
Once per turn: You can destroy 1 monster in your hand or field, and if you do, send 1 "Doll Monster" card from your Deck to the GY, also you cannot Special Summon monsters from the Extra Deck for the rest of this turn, except Xyz Monsters
I didn't reflect that much on the name change, but it was recently pointed out to me on this blog that sphere of annihilation was an artifact in D&D made famous by the 1978 module Tomb of Horrors, and it is possible that they changed the name before print to avoid any conflicts regarding intellectual property
Heavy Storm destroys all Spell and Trap cards on the field, including your own
The experience and skill needed to pilot some decks are extremely high, while others are straightforward