Agatha of the Vile Cauldron

Activated abilities of creatures you control cost {X} less to activate, where X is Agatha of the Vile Cauldron's power. This effect can't reduce the mana in that cost to less than one mana.
{4}{R}{G}: Other creatures you control get +1/+1 and gain trample and haste until end of turn.

Arni Brokenbrow

Haste
Boast — {1}: You may change Arni Brokenbrow's base power to 1 plus the greatest power among other creatures you control until end of turn. (Activate only if this creature attacked this turn and only once each turn.)

Bog Initiate

Captivating Crew

{3}{R}: Gain control of target creature an opponent controls until end of turn. Untap that creature. It gains haste until end of turn. Activate only as a sorcery.

Lightning Berserker

{R}: Lightning Berserker gets +1/+0 until end of turn.
Dash {R} (You may cast this spell for its dash cost. If you do, it gains haste, and it's returned from the battlefield to its owner's hand at the beginning of the next end step.)

Blood Celebrant

{B}, Pay 1 life: Add one mana of any color.

Rakdos Trumpeter

Menace (This creature can't be blocked except by two or more creatures.)
{3}{R}: Rakdos Trumpeter gets +2/+0 until end of turn.

Igneous Cur

{1}{R}: Igneous Cur gets +2/+0 until end of turn.

Locthwain Gargoyle

{4}: Locthwain Gargoyle gets +2/+0 and gains flying until end of turn.

Dragon Whisperer

{R}: Dragon Whisperer gains flying until end of turn.
{1}{R}: Dragon Whisperer gets +1/+0 until end of turn.
Formidable — {4}{R}{R}: Create a 4/4 red Dragon creature token with flying. Activate only if creatures you control have total power 8 or greater.

Varragoth, Bloodsky Sire

Deathtouch
Boast — {1}{B}: Target player searches their library for a card, then shuffles and puts that card on top. (Activate only if this creature attacked this turn and only once each turn.)

Wandering Goblins

Domain — {3}: Wandering Goblins gets +1/+0 until end of turn for each basic land type among lands you control.

Dynaheir, Invoker Adept

Haste
You may activate abilities of other creatures you control as though those creatures had haste.
{T}: When you next activate an ability that isn't a mana ability this turn by spending four or more mana to activate it, copy that ability. You may choose new targets for the copy.

Duergar Mine-Captain

{1}{R/W}, {Q}: Attacking creatures get +1/+0 until end of turn. ({Q} is the untap symbol.)

Manaforge Cinder

{1}: Add {B} or {R}. Activate no more than three times each turn.

Soltari Crusader

Shadow (This creature can block or be blocked by only creatures with shadow.)
{1}{W}: Soltari Crusader gets +1/+0 until end of turn.

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this turn.

Have

Zirda, the Dawnwaker

Companion — Each permanent card in your starting deck has an activated ability. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
Abilities you activate that aren't mana abilities cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.
{1}, {T}: Target creature can't block this turn.

Seafloor Stalker

{4}{U}: Seafloor Stalker gets +1/+0 until end of turn and can't be blocked this turn. This ability costs {1} less to activate for each creature in your party. (Your party consists of up to one each of Cleric, Rogue, Warrior, and Wizard.)

Vindictive Flamestoker

Whenever you cast a noncreature spell, put an oil counter on Vindictive Flamestoker.
{6}{R}, Sacrifice Vindictive Flamestoker: Discard your hand, then draw four cards. This ability costs {1} less to activate for each oil counter on Vindictive Flamestoker.

Horizon Seeker

Boast — {1}{G}: Search your library for a basic land card, reveal it, put it into your hand, then shuffle. (Activate only if this creature attacked this turn and only once each turn.)

Rampaging Raptor

Trample, haste
{2}{R}: Rampaging Raptor gets +2/+0 until end of turn.
Whenever Rampaging Raptor deals combat damage to an opponent, it deals that much damage to target planeswalker that player controls or battle that player protects.

Umbral Mantle

Equipped creature has "{3}, {Q}: This creature gets +2/+2 until end of turn." ({Q} is the untap symbol.)
Equip {0}

Forgestoker Dragon

Flying
{1}{R}: Forgestoker Dragon deals 1 damage to target creature. That creature can't block this combat. Activate only if Forgestoker Dragon is attacking.

Stonework Packbeast

Stonework Packbeast is also a Cleric, Rogue, Warrior, and Wizard.
{2}: Add one mana of any color.

Firehoof Cavalry

{3}{R}: Firehoof Cavalry gets +2/+0 and gains trample until end of turn.

Myr Welder

Imprint — {T}: Exile target artifact card from a graveyard.
Myr Welder has all activated abilities of all cards exiled with it.

Compleated Conjurer

When this creature transforms into Compleated Conjurer, exile the top card of your library. Until the end of your next turn, you may play that card.

Captive Weird

Defender
{3}{R/P}: Transform Captive Weird. Activate only as a sorcery. ({R/P} can be paid with either {R} or 2 life.)

Captive Weird // Compleated Conjurer

Hateflayer

Wither (This deals damage to creatures in the form of -1/-1 counters.)
{2}{R}, {Q}: Hateflayer deals damage equal to its power to any target. ({Q} is the untap symbol.)

Staff of Domination

{1}: Untap Staff of Domination.
{2}, {T}: You gain 1 life.
{3}, {T}: Untap target creature.
{4}, {T}: Tap target creature.
{5}, {T}: Draw a card.

Hate Weaver

{2}: Target blue or red creature gets +1/+0 until end of turn.

Tazri, Stalwart Survivor

Each creature you control has "{T}: Add one mana of any of this creature's colors. Spend this mana only to activate an ability of a creature. Activate only if this creature has another activated ability."
{W}{U}{B}{R}{G}, {T}: Mill five cards. Put all creature cards with activated abilities that aren't mana abilities from among the milled cards into your hand.

Inner-Flame Igniter

{2}{R}: Creatures you control get +1/+0 until end of turn. If this is the third time this ability has resolved this turn, creatures you control gain first strike until end of turn.

Sol Ring

Inferno of the Star Mounts

This spell can't be countered.
Flying, haste
{R}: Inferno of the Star Mounts gets +1/+0 until end of turn. When its power becomes 20 this way, it deals 20 damage to any target.

Weaselback Redcap

{1}{R}: Weaselback Redcap gets +2/+0 until end of turn.

Jenson Carthalion, Druid Exile

Whenever you cast a multicolored spell, scry 1. If that spell was all colors, create a 4/4 white Angel creature token with flying and vigilance.
{5}, {T}: Add {W}{U}{B}{R}{G}.

Lavafume Invoker

{8}: Creatures you control get +3/+0 until end of turn.

Amphin Pathmage

{2}{U}: Target creature can't be blocked this turn.

Two-Headed Dragon

Flying
Menace (This creature can't be blocked except by two or more creatures.)
Two-Headed Dragon can block an additional creature each combat.
{1}{R}: Two-Headed Dragon gets +2/+0 until end of turn.

Aetherling

{U}: Exile Aetherling. Return it to the battlefield under its owner's control at the beginning of the next end step.
{U}: Aetherling can't be blocked this turn.
{1}: Aetherling gets +1/-1 until end of turn.
{1}: Aetherling gets -1/+1 until end of turn.

Basalt Monolith

Basalt Monolith doesn't untap during your untap step.
{T}: Add {C}{C}{C}.
{3}: Untap Basalt Monolith.

Patrol Signaler

{1}{W}, {Q}: Create a 1/1 white Kithkin Soldier creature token. ({Q} is the untap symbol.)

Ogre Menial

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{R}: Ogre Menial gets +1/+0 until end of turn.

Phoenix of Ash

Flying, haste
{2}{R}: Phoenix of Ash gets +2/+0 until end of turn.
Escape—{2}{R}{R}, Exile three other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)
Phoenix of Ash escapes with a +1/+1 counter on it.

Najeela, the Blade-Blossom

Whenever a Warrior attacks, you may have its controller create a 1/1 white Warrior creature token that's tapped and attacking.
{W}{U}{B}{R}{G}: Untap all attacking creatures. They gain trample, lifelink, and haste until end of turn. After this phase, there is an additional combat phase. Activate only during combat.

Viashino Branchrider

Kicker {2}{G} (You may pay an additional {2}{G} as you cast this spell.)
Haste
If Viashino Branchrider was kicked, it enters the battlefield with two +1/+1 counters on it.
{2}{R}: Viashino Branchrider gets +2/+0 until end of turn.

Snow-Covered Wastes

Savage Knuckleblade

{2}{G}: Savage Knuckleblade gets +2/+2 until end of turn. Activate only once each turn.
{2}{U}: Return Savage Knuckleblade to its owner's hand.
{R}: Savage Knuckleblade gains haste until end of turn.

Agent of Stromgald

Dragonkin Berserker

First strike
Boast abilities you activate cost {1} less to activate for each Dragon you control.
Boast — {4}{R}: Create a 5/5 red Dragon creature token with flying. (Activate only if this creature attacked this turn and only once each turn.)