On your upkeep, you get to reveal cards from the top of your library until you reveal a Creature or Planeswalker card, then put it directly into play under your control
Legality depends on the tournament format -- Exsanguinate can be legal in some formats and banned or restricted in others
Fortunately, MTG 's green and white colors have a lot to offer
Besides a reliable flicker effect, Thassa also makes for a well-sized attacking creature as long as you can get enough blue permanents in play
That said, there are still plenty of new options for the format here
This is an extremely open-ended ability, rewarding you for milling yourself or your opponents, or even just for playing the game and removing powerful bomb creatures, by putting a must-kill threat into play for just five mana