
Land
As this land enters, you may reveal a Swamp or Forest card from your hand. If you don't, this land enters tapped.
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BG check land entering untapped with basic Swamp/Forest in play.

BG filter land producing both colors reliably.

BG shock land with basic land types for fetching.

BG painland always entering untapped for fast mana.

BG dual that taps for both if you control a Swamp.

BG fast land untapped early in the game.

Fetchland that grabs Swamp or Forest types for BG fixing.
If an effect instructs you to put one of these lands onto the battlefield tapped, it will still enter the battlefield tapped even if you reveal a land card from your hand.
You may reveal any land card with either or both of the appropriate subtypes. It doesn't have to be a basic land card.
The "Snarl" itself doesn't have any land subtypes. You can't reveal one to satisfy the ability of another.
If a land card with an appropriate subtype is entering the battlefield from your hand at the same time as one of these lands, you may reveal the other land to have the "Snarl" enter untapped.