The key with Construct2 instance selection is "picking" (read about it in manual, its essential). Basically you need to make sure you are picking the instance you want to be doing something, otherwise it picks all instances of the type specified. You pick instances using conditions in your events. In Bloodshot's example you are picking the "visible" sprite to act on. You can pick using basically anything that singles out a specific object... closest, furthest, visible, X-visible, on-screen, X-on-screen, UID, instance variables, etc. to name just a few.