Infinite colored mana that can only be spent to activate abilities of certain creaturesInfinite colored mana that can only be spent to cast spells of a certain creature typeInfinitely large creatures you control until end of turn
How it works
Activate Woodland Weavemaster by tapping it, adding an amount of G/W equal to its power that can only be spent to activate abilities of Elves or to cast Elf spells.
Activate Seedcradle Witch by paying 2, untapping Woodland Weavemaster and giving it +3/+3 until end of turn.
Repeat, alternating between adding and each loop as needed.