Agatha's Soul Cauldron

You may spend mana as though it were mana of any color to activate abilities of creatures you control.
Creatures you control with +1/+1 counters on them have all activated abilities of all creature cards exiled with Agatha's Soul Cauldron.
{T}: Exile target card from a graveyard. When a creature card is exiled this way, put a +1/+1 counter on target creature you control.

Shinryu, Transcendent Rival

Flying
As this creature transforms into Shinryu, choose an opponent.
Burning Chains — When the chosen player loses the game, you win the game.

Zenos yae Galvus

My First Friend — When Zenos yae Galvus enters, choose a creature an opponent controls. Until end of turn, creatures other than Zenos yae Galvus and the chosen creature get -2/-2.
When the chosen creature leaves the battlefield, transform Zenos yae Galvus.

Zenos yae Galvus // Shinryu, Transcendent Rival

Overkill

Target creature gets -0/-9999 until end of turn.

Torment of Hailfire

Repeat the following process X times. Each opponent loses 3 life unless that player sacrifices a nonland permanent of their choice or discards a card.

Murder

Sudden Death

Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
Target creature gets -4/-4 until end of turn.

Phage the Untouchable

When Phage enters, if you didn't cast it from your hand, you lose the game.
Whenever Phage deals combat damage to a creature, destroy that creature. It can't be regenerated.
Whenever Phage deals combat damage to a player, that player loses the game.