The Forest Blocker

Reach, when The Forest Blocker enters the battlefield, place one tree counter on it.
When you play a forest, place one tree counter on The Forest Blocker and remove one if you play a swamp.
Remove 6 tree counters Create 4 green and black creature tokens named "Dark Tree" with Reach, Defender, and "{t}: Add {b} or {g}." with +0/+4 (You can use this as an instant), then sacrifice them after.
If The Forest Blocker has no tree counters, then sacrifice The Forest Blocker and create one dark tree creature t