Splinter Twin + Devoted Druid + Cathars' Crusade

Splinter Twin

Devoted Druid

Cathars' Crusade

How it works

1. Activate Devoted Druid by tapping it, creating a token copy of it with haste.
2. When the Devoted Druid token enters the battlefield, Cathars' Crusade triggers, putting a +1/+1 counter on each creature you control.
3. Activate the nontoken Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it.
4. Repeat.
5. Once you have infinite Devoted Druid tokens, you may tap them to get infinite .

By enchanting Devoted Druid with Splinter Twin, you gain the ability to spawn an endless army of hasty token copies simply by tapping it. But to keep the loop going without running out of taps, the nontoken Devoted Druid uses its own built-in ability to place a -1/-1 counter on itself to untap, perfectly resetting for the next activation. Meanwhile, every newly born token triggers Cathars' Crusade upon entering the battlefield, steadily distributing +1/+1 counters that instantly offset the Druid's -1/-1 counters and permanently pump your entire board to monstrous proportions.