Fellwar Stone

{T}: Add one mana of any color that a land an opponent controls could produce.

Ozox, the Clattering King

Ozox can't block.
When Ozox dies, create Jumblebones, a legendary 2/1 black Skeleton creature token with "Jumblebones can't block" and "When Jumblebones leaves the battlefield, return target card named Ozox, the Clattering King from your graveyard to your hand."

Mahadi, Emporium Master

At the beginning of your end step, create a Treasure token for each creature that died this turn. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Ashnod's Altar

Meren of Clan Nel Toth

Whenever another creature you control dies, you get an experience counter.
At the beginning of your end step, choose target creature card in your graveyard. If that card's mana value is less than or equal to the number of experience counters you have, return it to the battlefield. Otherwise, put it into your hand.

Sol Ring

Sek'Kuar, Deathkeeper

Whenever another nontoken creature you control dies, create a 3/1 black and red Graveborn creature token with haste.

Honest Rutstein

When Honest Rutstein enters, return target creature card from your graveyard to your hand.
Creature spells you cast cost {1} less to cast.