Effect
You can send 1 Plant-Type monster from your hand or face-up from your side of the field to the Graveyard; choose 1 "Sylvan" card from your Deck and place it on top of the Deck. You can only use this effect of "Mount Sylvania" once per turn. Once per turn, during your opponent's End Phase: You can excavate the top card of your Deck, and if it is a Plant-Type monster, send it to the Graveyard. Otherwise, place it on either the top or bottom of your Deck.
You cannot activate the effect to "choose 1 'Sylvan' card from your Deck and place it on top of the Deck" in the same chain block as the activation of the "Mount Sylvania" card itself.
When activating the effect to "choose 1 'Sylvan' card from your Deck and place it on top of the Deck," you must send 1 Plant-Type monster from your hand or face-up on your side of the field to the Graveyard as a cost.
The effect to "once per turn, during your opponent's End Phase, you can excavate the top card of your Deck" is an effect that creates a chain block.
Excavating the Deck with the effect to "once per turn, during your opponent's End Phase, you can excavate the top card of your Deck" is not a cost. It is part of the effect resolution.
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