You may sacrifice any two lands with the subtype Island to activate Biolume Serpent's ability, even if they aren't basic or aren't named Island
It's a game-ender, typically sweeping away your opponent's entire board, while preserving any colorless permanents you've chosen to play, and, more often than not, also leaving Ugin alive to keep pecking away with their +2 damage-dealing power
Bitterblossom is not what you want to see late and it can be tough to get out early if under pressure
There are three primary ways to win with tokens: You attack with enough creature tokens that your opponent cant possibly hope to block them all, You pair your token generation with Mirkwood Bats, Impact Tremors, Zulaport Cutthroat, and similar effects that drain your opponents life total as your tokens enter and leave the battlefield, or You have sacrifice outlets that let you cash in tokens to kill blockers and/or drain your opponents life, like Goblin Bombardment