Bioessence Hydra

Trample
Bioessence Hydra enters with a +1/+1 counter on it for each loyalty counter on planeswalkers you control.
Whenever one or more loyalty counters are put on planeswalkers you control, put that many +1/+1 counters on Bioessence Hydra.

War of the Spark

War of the Spark Promos

Abilities that trigger when counters are put on a permanent trigger when a permanent enters the battlefield with counters and when a player puts counters on a permanent.

If Bioessence Hydra enters the battlefield at the same time as a planeswalker you control, the loyalty counters that planeswalker will receive won’t be counted to determine how many counters Bioessence Hydra enters the battlefield with, but they will cause its last ability to trigger.