Seeker of Slaanesh

Haste
Allure of Slaanesh — Each opponent must attack with at least one creature each combat if able.

Seeker

Enchant creature
Enchanted creature can't be blocked except by artifact creatures and/or white creatures.

Guttersnipe

Whenever you cast an instant or sorcery spell, this creature deals 2 damage to each opponent.

Siphon Insight

Look at the top two cards of target opponent's library. Exile one of them face down and put the other on the bottom of that library. You may play the exiled card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell.
Flashback {1}{U}{B}

Fight

Aftermath (Cast this spell only from your graveyard. Then exile it.)
Target creature you control fights target creature an opponent controls.

Prepare

Untap target creature. It gets +2/+2 and gains lifelink until end of turn.

Prepare // Fight

Make Your Move

Destroy target artifact, enchantment, or creature with power 4 or greater.

Defense Grid

Each spell costs {3} more to cast except during its controller's turn.

Murderous Betrayal

{B}{B}, Pay half your life, rounded up: Destroy target nonblack creature. It can't be regenerated.

Double Cleave

Target creature gains double strike until end of turn. (It deals both first-strike and regular combat damage.)

Sure Strike

Target creature gets +3/+0 and gains first strike until end of turn. (It deals combat damage before creatures without first strike.)