Summoning Sickness

[TheJord]

When crits hit play, can they be used by other crits abilities, or things like conspire?

[SomeRandomDude]

Yes. They simply cannot use abilities or attack when they hit play.

Hence why Gemhide Slivers can't be used to play out a chain of 1 drop slivers.
Also why Drowner of Secrets CAN be used to mill the turn it hits play. Or any other merfolk hits play.

[FM]

Since the tags didn't quite work out, let me clarify. Any ability on THAT creature with the tap symbol can't be used (unless the creature has haste). Any ability that says: "tap a(n) (untapped) ____", like Conspire or, as NBarden explained, Drowner of Secrets, CAN be used, even by themselves. Since there's no tap simbol, it's considered to be the same as a repeatable ability with a cost, and those can always be used pronto.