Your new Active Pokmon takes its place
TheChirurgeon: The tokens also replicating can make this super nasty, though the (smart) second card restriction means you'll only ever get this once per turn
While we dont have full information yet about how the card works mechanically, theres plenty of room for speculation
It works particularly well in this archetype because leave the graveyard cards are often triggered by other things that generate an advantage: You might return creatures to your hand with a Regrowth, reanimate a creature, play lands from your graveyard, etc
Enchanting an opponents land to deal damage whenever it becomes tapped can help to trigger Valgavoth, while also locking down an opponents utility land or just keeping them behind the curve
That's why permanents such as Consecrated Sphinx or Mind's Eye are so valuable