Unfortunately, the way COs are made, making them solid or hurtful is simply not going work right out of the box. The detection used for the COs does NOT match the shape of the sprite, and thus, it won't be solid were you want, or hurt where you want. (I've tried this on KSA, just trust me) The only way to make this work is to somehow 1: Redo the COs engine so that it supports collisions like it should, or somehow make the detections work with current engine. Both of these are very hard options, and I'm afraid it isn't going to be done quickly by anyone. Having said that, tho. A solid custom object (that does make the image solid) is a bad idea, simply because it is just going to give you wallswims if animated anyway.