The combination of Amalia and an indestructible Wildgrowth Walker always draws the game with an infinite loop once a creature explores, no matter what card is on top of the library.
For reference, Amalia has the text
Whenever you gain life, Amalia Benavides Aguirre explores. Then destroy all other creatures if its power is exactly 20.
and Wildgrowth Walker has the text
Whenever a creature you control explores, put a +1/+1 counter on this creature and you gain 3 life.
The keyword action “explore” and the event “explores” are defined in rules 701.40a-b:
701.40a. Certain abilities instruct a permanent to explore. To do so, that permanent’s controller reveals the top card of their library. If a land card is revealed this way, that player puts that card into their hand. Otherwise, that player puts a +1/+1 counter on the exploring permanent and may put the revealed card into their graveyard.
701.40b. A permanent “explores” after the process described in rule 701.40a is complete, even if some or all of those actions were impossible.
So, if a player controls Amalia and a Wildgrowth Walker, and a creature explores, then Wildgrowth Walker’s ability triggers, which causes the player to gain life, so Amalia’s ability triggers, and she explores, which triggers Wildgrowth Walker’s ability again, in a loop. The only choice any player makes during that process is what to do with the card on top of the library, if it is not a land.
However, because of the last part of rule 701.40b, the exploration happens no matter what card is on top of the library, and even if there is no card on top of the library at all. This means that the loop always continues, no matter what choice the player makes while exploring. Therefore, the loop is mandatory, so the game is a draw.