Magus of the Abyss

At the beginning of each player's upkeep, destroy target nonartifact creature that player controls of their choice. It can't be regenerated.

Barrenton Medic

{T}: Prevent the next 1 damage that would be dealt to any target this turn.
Put a -1/-1 counter on this creature: Untap this creature.

{T}: Add {G}.
Put a -1/-1 counter on this creature: Untap this creature.

All creatures have "At the beginning of your upkeep, sacrifice this creature unless you pay {1}."

Constellation — Whenever an enchantment you control enters, put a +1/+1 counter on this creature and draw a card.

If one or more -1/-1 counters would be put on a creature you control, that many -1/-1 counters minus one are put on it instead.

Constellation — Whenever this creature or another enchantment you control enters, draw a card.

{T}: Target player discards a card. Activate only during your turn.
Put a -1/-1 counter on this creature: Untap this creature.