Impervious Greatwurm

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.)
Indestructible

Simic Ragworm

Elderscale Wurm

Trample
When Elderscale Wurm enters the battlefield, if your life total is less than 7, your life total becomes 7.
As long as you have 7 or more life, damage that would reduce your life total to less than 7 reduces it to 7 instead.

Cryptic Annelid

When Cryptic Annelid enters the battlefield, scry 1, then scry 2, then scry 3. (To scry X, look at the top X cards of your library, then put any number of them on the bottom of your library and the rest on top in any order.)

Feast of Worms

Destroy target land. If that land was legendary, its controller sacrifices another land.