Undercity Reaches

Instant and sorcery cards in graveyards have flashback. The flashback cost is equal to the card's mana cost. (Its owner may cast the card from their graveyard for its mana cost. Then they exile it.) Whenever chaos ensues, take an extra turn after this one.

All creatures have wither. (They deal damage to creatures in the form of -1/-1 counters.) Whenever chaos ensues, put a -1/-1 counter on target creature, two -1/-1 counters on another target creature, and three -1/-1 counters on a third target creature.

All creatures have exalted. (Whenever a creature attacks alone, it gets +1/+1 until end of turn for each instance of exalted among permanents its controller controls.) Whenever chaos ensues, put a divinity counter on target green, white, or blue creature. That creature has indestructible for as long as it has a divinity counter on it.

If a source would deal damage to a permanent or player, it deals double that damage instead. Whenever chaos ensues, Stronghold Furnace deals 1 damage to any target.

Whenever a player casts a spell, that player may draw a card. Whenever chaos ensues, each player may return a blue card from their graveyard to their hand.

When you planeswalk to Cliffside Market and at the beginning of your upkeep, you may exchange life totals with target player. Whenever chaos ensues, exchange control of two target permanents that share a card type.

Whenever a nonblack card is put into a player's graveyard from anywhere, that player loses 1 life. Whenever chaos ensues, each opponent discards a card.

When you planeswalk to The Aether Flues and at the beginning of your upkeep, you may sacrifice a creature. If you do, reveal cards from the top of your library until you reveal a creature card, put that card onto the battlefield, then shuffle all other cards revealed this way into your library. Whenever chaos ensues, you may put a creature card from your hand onto the battlefield.