Magus da Ordem

If Magus of the Order becomes nongreen, you can still activate its ability by sacrificing it and a green creature.

Once you declare you're activating the ability, players can't take any actions until you've finished doing so. Notably, opponents can't try to remove Magus of the Order or green creatures you control to stop you from activating the ability.

You can't sacrifice additional creatures to search for more green creatures.