Infinite creature tokens with hasteInfinite creature ETBInfinite green manaInfinite +1/+1 counters on creatures you control
How it works
Activate Devoted Druid by tapping it, creating at least two 1/1 Elemental creature tokens with haste.
When the Elementals enters the battlefield, Cathars' Crusade trigger that many times, putting that many +1/+1 counters on each creature you control.
Activate Devoted Druid by putting a -1/-1 counter on it, untapping it.
Repeat.
If Devoted Druid has a power of two or greater, you then get infinite +1/+1 counters on Devoted Druid, which you may use to activate its mana ability instead to get infinite .