Necrotic Ooze + Kjeldoran Elite Guard + Devoted Druid

Necrotic Ooze

Kjeldoran Elite Guard

Devoted Druid

How it works

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

This clever combination turns Necrotic Ooze into a one-stop engine by scavenging the activated abilities of creatures resting in the graveyard. While the text borrowed from Kjeldoran Elite Guard provides the tap ability to jump-start the loop, Devoted Druid supplies the crucial mechanic of untapping itself by placing a -1/-1 counter. Because Necrotic Ooze absorbs these traits, you can repeatedly untap the Ooze to pump its toughness to astronomical heights, and then pivot to tapping it for green mana once it is safely out of harm's reach.