"Subterror Behemoth Ultramafus" has the highest Level and original ATK of all Flip monsters, being Level 12 with 3000 ATK
[1] Once per turn, when another card effect is activated (Quick Effect): You can negate that activation, and if you do, destroy it, then if a monster was destroyed, this card gains ATK equal to the destroyed card's original ATK until the end of the turn
Especially in faster formats like cEDH, this inconspicuous Conqueror punishes opponents for trying to play the game on curve, all while quietly adding little Lifelinkers to your board
add it to your hand, then, if "The Sanctuary in the Sky" is on the field or in either GY, you can add 1 of your banished "The Sanctuary in the Sky", or 1 of your banished cards that mentions it, to your hand