Undead, Mountain Climbers

Through the forest, up the mountains — Tap a forest
to add {r}{r}.

Through the forest — When a zombie you control
dies, search your library for a forest, reaveal it
and put it in your hand.

Zombies ascend the mountain — When you attack,
you may sacrafice a zombie and create a tapped
and attacking black zombie creature token with
haste and decayed.