Three Steps Ahead

Spree (Choose one or more additional costs.)
+ {1}{U} — Counter target spell.
+ {3} — Create a token that's a copy of target artifact or creature you control.
+ {2} — Draw two cards, then discard a card.

Arcane Denial

Counter target spell. Its controller may draw up to two cards at the beginning of the next turn's upkeep.
You draw a card at the beginning of the next turn's upkeep.

Goblin Electromancer

Instant and sorcery spells you cast cost {1} less to cast.

Boggart Shenanigans

Whenever another Goblin you control is put into a graveyard from the battlefield, you may have this enchantment deal 1 damage to target player or planeswalker.

Counterspell

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Zinnia, Valley's Voice

Flying
Zinnia gets +X/+0, where X is the number of other creatures you control with base power 1.
Creature spells you cast have offspring {2}. (You may pay an additional {2} as you cast a creature spell. If you do, when that creature enters, create a 1/1 token copy of it.)

Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

Goblin Chainwhirler

First strike
When this creature enters, it deals 1 damage to each opponent and each creature and planeswalker they control.

Young Pyromancer

Whenever you cast an instant or sorcery spell, create a 1/1 red Elemental creature token.

Goblin Matron

When this creature enters, you may search your library for a Goblin card, reveal that card, put it into your hand, then shuffle.

Mana Leak

Counter target spell unless its controller pays {3}.

Goblin Fireslinger

{T}: This creature deals 1 damage to target player or planeswalker.

Gamble

Search your library for a card, put that card into your hand, discard a card at random, then shuffle.

Imperial Recruiter

When this creature enters, search your library for a creature card with power 2 or less, reveal it, put it into your hand, then shuffle.

Dragonmaster Outcast

At the beginning of your upkeep, if you control six or more lands, create a 5/5 red Dragon creature token with flying.

Akki Rockspeaker

Dispel

Mogg Mob

Sacrifice this creature: It deals 3 damage divided as you choose among one, two, or three targets.

Rootborn Defenses

Populate. Creatures you control gain indestructible until end of turn. (To populate, create a token that's a copy of a creature token you control.)