Lake of the Dead has quite an expensive effect, forcing you to sacrifice a Swamp just to get it onto the field (the idea, I think, is for a Swamp to flow over and turn into the Lake) and then you can sacrifice another Swamp for four times of the mana
Every time one of your creatures dies, you gain a counter that never goes away, and during your end step, Meren brings a creature back from the graveyard to your hand or directly to the battlefield if your counter count is high enough
For example, the last ability will count experience counters that you got from the second ability, from another ability, from another copy of Aang, Airbending Master, and so on
But what exactly dictates "imperfection"
La carte Keldeo GX, numrote 240/236, fait partie de la srie SL Harmonie des Esprits