Wildborn Preserver
Creature — Elf Archer
Flash (You may cast this spell any time you could cast an instant.)
Reach (This creature can block creatures with flying.)
Whenever another non-Human creature you control enters, you may pay 
. When you do, put X +1/+1 counters on this creature.
Lius Lasahido
Throne of Eldraine (ELD)
• #375Rulings
If you pay {X} while Wildborn Preserver's triggered ability is resolving, the reflexive triggered ability triggers and will resolve separately. This is different from effects that say “If you do . . .” in that players may take actions after you've paid mana but before the creature gets +1/+1 counters.
(wotc • 2019-10-04)
Rulings
If you pay {X} while Wildborn Preserver's triggered ability is resolving, the reflexive triggered ability triggers and will resolve separately. This is different from effects that say “If you do . . .” in that players may take actions after you've paid mana but before the creature gets +1/+1 counters.
(wotc • 2019-10-04)