Scyllus' Guardian

Scyllus' Guardian enters the battlefield with a number of +1/+1 counters equal to the amount of mana spent to cast it.
Hydra creatures you control have trample and hexproof.
{r/g}{r/g}{r/g}{r/g}{r/g}: Another target hydra you control gets +X/+X until end of turn, where X is equal to the number of counters on that creature. Activate this ability only once each turn.