Merciless Executioner

When this creature enters, each player sacrifices a creature of their choice.

Fleshbag Marauder

Sol Ring

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.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Caustic Caterpillar

{1}{G}, Sacrifice this creature: Destroy target artifact or enchantment.

Spore Frog

Sacrifice this creature: Prevent all combat damage that would be dealt this turn.

Sakura-Tribe Elder

Sacrifice this creature: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.