the 0 and the 1 are the ones hitting eachother, 0 being the one you control (or even if you dont control it) please tell me if you dont understand something! BG collision is a bit harder, i can give you two files i made if you want, or i can try to explain, see there are two main types of BG collision, there is with a non moving background and there is with a background moved with BGOFS. ↓maps↓