Muck's Best Friend

Delve (Each card you exile from your graveyard
while casting this spell pays for {1}).
Create an indestructible legendary X/X
green Elemental named 'Compost', where
X is the number of cards you own in exile.
"Muck whispered incomprehensible songs onto the
surface of the water, sparking the delight of the depths.
His face showed nothing but glee as the heart of the
Wetland itself arose from the water to greet him."