Desert Were-Worm

This creature gets +2/+0 for each Mountain you control. Whenever you attack with creatures with total power 12 or greater for the first time each turn, untap all attacking creatures. After this phase, there is an additional combat phase.

From Magic: The Gathering.

Open the interactive version on https://mythscribe.cloud/app/tcg/cards/cms6o91fm5up1pb1hsm65b9ef.