Currently, these infinite mana situations came to my mind:
#1: Mirror Entity + Nettle Sentinel + Heritage Druid + Wirewood Symbiote
#2: Mirror Entity + Priest of Titania + Wirewood Symbiote
#3: Mirror Entity + Heritage Druid + Wirewood Symbiote + Wirewood Symbiote
I know I might miss some but I don't know them all off the bat.
Since I'm too lazy to explain them in detail:
Basically, in every situation you activate Entity for 1 to make the Symbiotes creature type "Elf" so they can tap for mana or Priest produces more mana...then you can also bounce the Symbiotes themselves since they are Elves. Then you can replay Symbiote.
This results in at least 1 extra mana left each time you do that. Meanwhile you untapped a creature with the symbiote effect and you are able to continue to tap for mana and use the Symbiote bounce again while ending up with an extra mana in the end
-> infinite
-> kill with big guys