Deadeye's solutions are good so far, except that you can do it without subevents, heh - 'pick random' could simply be a condition after 'every'.
As for object picking via conditions, remember two things:
- For Each works best as the first condition
- Use built-in conditions wherever possible instead of System's Compare Values (eg. Sprite's Compare X rather than comparing Sprite.X to a value - works instance by instance)
Also might help to post your .cap file, so I can tell you exactly what's going on.