Infinite creature tokens with hasteInfinite creature ETBInfinite green manaInfinitely large creature until end of turn
How it works
Activate Devoted Druid by tapping it, creating at least one 1/1 Elemental creature token with haste.
When the Elemental token(s) enter the battlefield, Devoted Druid triggers that many times, giving it +1/+1 until end of turn for each creature that entered the battlefield.
Activate Devoted Druid by putting a -1/-1 counter on it, untapping it.
Repeat.
If Devoted Druid has a power of two or greater, Devoted Druid becomes infinitely large until end of turn, which allows you to use its mana ability instead to get infinite .