With all cards in play:
Tap Devoted Druid to add a green mana
Put a -1/-1 counter on Devoted Druid to untap it
Flourishing Defenses ability will trigger, create an Elf token
Ivy Lane Denizen's ability will trigger, put a +1/+1 counter on Devoted Druid
+1/+1 and -1/-1 counters cancel each other out
Repeat the process for infinite mana and infinite tokens.