You may pay WUBRG rather than pay this spell s mana cost. If you do, X is 5.

Bringer of Green Zenith s Twilight enters the battlefield with X +1/+1 counters on it. If X was 5 or greater, it enters with twice that many counters instead.

When Bringer of Green Zenith s Twilight dies, shuffle it into its owner s library.