Thopter Squadron has at least two +1/+1 counters on it.
Steps
Activate Devoted Druid's first ability by tapping it, adding ({G} magic symbol) .
Activate Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it.
Activate Devoted Druid's first ability by tapping it, adding ({G} magic symbol) .
Activate Thopter Squadron's first ability by paying ({1} magic symbol) and removing a +1/+1 counter from it, creating a 1/1 Thopter artifact creature token.
When the Thopter enters the battlefield as a Treefolk due to Maskwood Nexus, Quickbeam triggers, giving Devoted Druid and up to one other creature +2/+2 until end of turn.
Activate Thopter Squadron's second ability by paying ({1} magic symbol) and sacrificing the Thopter, putting a +1/+1 counter on Thopter Squadron.
Activate Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it.
Repeat.
Results
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinitely large creatures until end of turn except Devoted Druid.