I suppose I should actually comment on the card itself too...
Zero cost is too cheap. Even at

, I think this is quite possibly too good. For balance reasons, this should probably say "non-token" creature.
You get pretty ridiculous interactions between this and stuff like Shrieking Drake. With multiples, you get stupid amounts of mana pretty quickly. For example, with two Hearts and a Drake:
T1: Island, Heart 1, Heart 2. Tap Island for Drake. Tap Heart 1 for

. Play Drake. Tap Heart 2 for

. Play Drake twice (2 counters on each Heart). You've now got 5 mana of any color available for T2 (3 counters on first Heart, 2 on the second), and can still ramp before casting any real spells.
T2: Tap Island for Drake. Tap first Heart, play Drake 4 times. Tap second Heart, get 7 blue. Play something pricey, say FOF. Use remaining

to play Drake. You now have 10 Heart mana available for T3 (7 counters & 3 counters). Pure ramp would have gotten you 18! Heart mana for T3.
After working out that scenario, this probably needs more nerfing. Maybe add only 1 mana per two counters removed?