But while we're at it, we'll add a few bells and whistles:

• By default, it will cycle through all the available costumes. But we'll also define animation_first_costume and animation_final_costume properties so we can choose to cycle through a subset of costumes.
• We'll define an animation_continuous property that controls whether the animation keeps looping, or just gets to animation_final_costume and then stops.

This will give us much more powerful and convenient costume animation than we get in Scratch.