Berta, Wise Extrapolator
{2}{G}{U}Legendary Creature — Frog Druid
Increment (Whenever you cast a spell, if the amount of mana you spent is greater than this creature's power or toughness, put a +1/+1 counter on this creature.) Whenever one or more +1/+1 counters are put on Berta, add one mana of any color. {X}, {T}: Create a 0/0 green and blue Fractal creature token and put X +1/+1 counters on it.