Urborg, Tomb of Yawgmoth

Each land is a Swamp in addition to its other land types.

Mountain

Tyrranax Rex

This spell can't be countered.
Trample, ward {4}, haste
Toxic 4 (Players dealt combat damage by this creature also get four poison counters.)

Tainted Strike

Target creature gets +1/+0 and gains infect until end of turn. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Badlands

Swamp

Sneak Attack

{R}: You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice the creature at the beginning of the next end step.

Restless Bones

{3}{B}, {T}: Target creature gains swampwalk until end of turn. (It can't be blocked as long as defending player controls a Swamp.)
{1}{B}: Regenerate Restless Bones.