Valley Carving Wurm

Convoke (Your creatures can help cast this spell.
Each creature you tap while casting this spell pays
for {1} or one mana of that creature's color.)
Trample
When Valley Carving Wurm attacks, you may
Valley counter on a target Mountain, it becomes
a Forest.
The most terrifying thing about the valley carving
wurm is the noise, So deep it can only be heard in the
bones and too loud for ears. Seeming to come from
all directions at once.