Cephalid Vandal

[mickeven]

would {Cephalid Vandal} trigger  {Sidisi, Brood Tyrant}'s ability for each counter on it, or just count as one time?

[particle]

would {Cephalid Vandal} trigger  {Sidisi, Brood Tyrant}'s ability for each counter on it, or just count as one time?

So vandal triggers and you mill x cards for x counters. This is one action you mill all the cards at the same. Sidisi will trigger once if any creatures were milled.