During your precombat main phase, activate Necrotic Ooze using Stern Marshal's ability by tapping it, giving it +2/+2 until end of turn.
Activate Necrotic Ooze using Barrenton Medic's second ability by putting a -1/-1 counter on it, untapping it.
Repeat.

Infinitely large creature until end of turn

Necrotic Ooze

Stern Marshal

Barrenton Medic

During your precombat main phase, activate Necrotic Ooze using Stern Marshal's ability by tapping it, giving it +2/+2 until end of turn.
Activate Necrotic Ooze using Cinderhaze Wretch's second ability by putting a -1/-1 counter on it, untapping it.
Repeat.

Cinderhaze Wretch

During your precombat main phase, activate Necrotic Ooze using Stern Marshal's ability by tapping it, giving it +2/+2 until end of turn.
Activate Necrotic Ooze using Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it.
Repeat.
Once Necrotic Ooze has infinite toughness, you may instead use Devoted Druid's first ability to get infinite green mana.

Combos with "Stern Marshal"