Gash, Kavina-Tribe Skyhunter

Deathtouch, Reach
Prowl {b/g}{b/g}{b/g}
When Gash, Kavina-Tribe Skyhunter enters the battlefield, if its prowl cost was paid, put X -1/-1 counters on target creature with flying, where X
is the amount of black mana used to cast Gash,
and put X +1/+1 counters on target Elf, where X
is the amount of green mana spent to cast Gash.