Darksteel Relic

Indestructible (Effects that say "destroy" don't destroy this artifact.)

Break Open

Turn target face-down creature an opponent controls face up.

Assembly Hall

{4}, {T}: Reveal a creature card in your hand. Search your library for a card with the same name as that card, reveal it, put it into your hand, then shuffle.

Crevasse

Creatures with mountainwalk can be blocked as though they didn't have mountainwalk.

Adventurers' Guildhouse

Green legendary creatures you control have "bands with other legendary creatures." (Any legendary creatures can attack in a band as long as at least one has "bands with other legendary creatures." Bands are blocked as a group. If at least two legendary creatures you control, one of which has "bands with other legendary creatures," are blocking or being blocked by the same creature, you divide that creature's combat damage, not its controller, among any of the creatures it's being blocked by or is blocking.)

Quagmire

Creatures with swampwalk can be blocked as though they didn't have swampwalk.

Arcum's Sleigh

{2}, {T}: Target creature gains vigilance until end of turn. Activate only during combat and only if defending player controls a snow land.

Tarox Bladewing

Flying, haste
Grandeur — Discard another card named Tarox Bladewing: Tarox Bladewing gets +X/+X until end of turn, where X is its power.

Swamp

Razor Boomerang

Equipped creature has "{T}, Unattach Razor Boomerang: It deals 1 damage to any target. Return Razor Boomerang to its owner's hand."
Equip {2}

Rakalite

{2}: Prevent the next 1 damage that would be dealt to any target this turn. Return Rakalite to its owner's hand at the beginning of the next end step.

Wintermoon Mesa

Wintermoon Mesa enters tapped.
{T}: Add {C}.
{2}, {T}, Sacrifice Wintermoon Mesa: Tap two target lands.

Hint of Insanity

Target player reveals their hand. That player discards all nonland cards with the same name as another card in their hand.

Relentless Rats

Relentless Rats gets +1/+1 for each other creature on the battlefield named Relentless Rats.
A deck can have any number of cards named Relentless Rats.

Sorrow's Path

{T}: Choose two target blocking creatures controlled by the same opponent. If each of those creatures could block all creatures that the other is blocking, remove both of them from combat. Each one then blocks all creatures the other was blocking.
Whenever Sorrow's Path becomes tapped, it deals 2 damage to you and each creature you control.

Dungeon Descent

Dungeon Descent enters tapped.
{T}: Add {C}.
{4}, {T}, Tap an untapped legendary creature you control: Venture into the dungeon. Activate only as a sorcery. (Enter the first room or advance to the next room.)

Armageddon Clock

At the beginning of your upkeep, put a doom counter on Armageddon Clock.
At the beginning of your draw step, Armageddon Clock deals damage equal to the number of doom counters on it to each player.
{4}: Remove a doom counter from Armageddon Clock. Any player may activate this ability but only during any upkeep step.

Mountain

Pretender's Claim

Enchant creature
Whenever enchanted creature becomes blocked, tap all lands defending player controls.