Treasure Nabber

Whenever an opponent taps an artifact for mana, gain control of that artifact until the end of your next turn.

Devilish Valet

Trample, haste
Alliance — Whenever another creature you control enters, double Devilish Valet's power until end of turn.

Shared Animosity

Whenever a creature you control attacks, it gets +1/+0 until end of turn for each other attacking creature that shares a creature type with it.

Elephant Grass

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Black creatures can't attack you.
Nonblack creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Mystic Remora

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Jodah, Archmage Eternal

Flying
You may pay {W}{U}{B}{R}{G} rather than pay the mana cost for spells you cast.

City on Fire

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.)
If a source you control would deal damage to a permanent or player, it deals triple that damage instead.

Maskwood Nexus

Creatures you control are every creature type. The same is true for creature spells you control and creature cards you own that aren't on the battlefield.
{3}, {T}: Create a 2/2 blue Shapeshifter creature token with changeling. (It is every creature type.)

Mana Echoes

Whenever a creature enters, you may add an amount of {C} equal to the number of creatures you control that share a creature type with it.

Sting, the Glinting Dagger

Equipped creature gets +1/+1 and has haste.
At the beginning of each combat, untap equipped creature.
Equipped creature has first strike as long as it's blocking or blocked by a Goblin or Orc.
Equip {2}

Tocasia's Dig Site

{T}: Add {C}.
{3}, {T}: Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Eternal Witness

When Eternal Witness enters, you may return target card from your graveyard to your hand.

Mesmeric Orb

Whenever a permanent becomes untapped, that permanent's controller mills a card.