Space Marine Devastator

Creature — Astartes Warrior

Squad (As an additional cost to cast this spell, you may pay any number of times. When this creature enters, create that many tokens that are copies of it.)

Grav-cannon — When this creature enters, destroy up to one target artifact or enchantment.

You may pay the squad cost any number of times. You will get a token that is a copy of that permanent for each time you paid the squad cost.
If the spell is countered, the squad ability will not trigger, and no tokens will be created.
The tokens created by the squad ability aren't "cast," so any abilities that trigger when a spell is cast won't trigger for the copies.
If, for some reason, the creature doesn't have the squad ability when it's on the battlefield, the ability won't trigger, even if you've paid the squad cost one or more times.