Gamble

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

Arni Metalbrow

Whenever a creature you control attacks or a creature you control enters attacking, you may pay {1}{R}. If you do, you may put a creature card with mana value less than that creature's mana value from your hand onto the battlefield tapped and attacking.

Bard Class

(Gain the next level as a sorcery to add its ability.)
Legendary creatures you control enter with an additional +1/+1 counter on them.
{R}{G}: Level 2
Legendary spells you cast cost {R}{G} less to cast. This effect reduces only the amount of colored mana you pay.
{3}{R}{G}: Level 3
Whenever you cast a legendary spell, exile the top two cards of your library. You may play them this turn.

Cait, Cage Brawler

During your turn, Cait has indestructible.
Whenever Cait attacks, you and defending player each draw a card, then discard a card. Put two +1/+1 counters on Cait if you discarded the card with the greatest mana value among those cards or tied for greatest.

Hajar, Loyal Bodyguard

Sacrifice Hajar: Legendary creatures you control get +1/+0 and gain indestructible until end of turn.

Anzrag, the Quake-Mole

Whenever Anzrag becomes blocked, untap each creature you control. After this phase, there is an additional combat phase.
{3}{R}{R}{G}{G}: Anzrag must be blocked each combat this turn if able.

Azusa, Lost but Seeking

You may play two additional lands on each of your turns.

Abstergo Entertainment

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
{3}, {T}, Exile Abstergo Entertainment: Return up to one target historic card from your graveyard to your hand, then exile all graveyards. (Artifacts, legendaries, and Sagas are historic.)

Ashling the Pilgrim

{1}{R}: Put a +1/+1 counter on Ashling. If this is the third time this ability has resolved this turn, remove all +1/+1 counters from Ashling, and it deals that much damage to each creature and each player.

Arasta of the Endless Web

Reach
Whenever an opponent casts an instant or sorcery spell, create a 1/2 green Spider creature token with reach.

Anax, Hardened in the Forge

Anax's power is equal to your devotion to red. (Each {R} in the mana costs of permanents you control counts toward your devotion to red.)
Whenever Anax or another nontoken creature you control dies, create a 1/1 red Satyr creature token with "This token can't block." If the creature had power 4 or greater, create two of those tokens instead.

Bessie, the Doctor's Roadster

Haste
Whenever Bessie attacks, another target legendary creature can't be blocked this turn.
Crew 2 (Tap any number of creatures you control with total power 2 or more: This Vehicle becomes an artifact creature until end of turn.)