Quickbeam, Upstart Ent + Devoted Druid + Spawnsire of Ulamog + Maskwood Nexus

Quickbeam, Upstart Ent

Devoted Druid

Spawnsire of Ulamog

Maskwood Nexus

How it works

1. Activate Spawnsire of Ulamog's first ability by paying 4, creating two 0/1 Eldrazi Spawn creature tokens.
2. When the Eldrazi Spawns enter the battlefield as Treefolk due to Maskwood Nexus, Quickbeam triggers twice, giving Devoted Druid and up to one other creature +4/+4 until end of turn.
3. Activate Devoted Druid's first ability by tapping it, adding .
4. Activate Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it.
5. Repeat from step 3 three additional times.
6. Repeat from step 1.

Maskwood Nexus is the crucial architectural piece here, transforming every creature you control into a Treefolk and Eldrazi so that the rest of the engine can recognize them. Once this tribal blanket is in place, paying to activate Spawnsire of Ulamog generates two Eldrazi Spawn tokens that simultaneously trigger Quickbeam, Upstart Ent's ability to pump your team. This massive influx of entering creatures lets you repeatedly tap Devoted Druid for green mana and untap it by placing -1/-1 counters on it, cleanly converting that mana into the colorless energy needed to fuel Spawnsire of Ulamog's token creation indefinitely.