Hey all, I've created a packet sniffer and lets say I've hooked up a game and can intercept all traffic, modify packets, replay etc. Now the question is, when I replay a packet, lets say Moving packet, how does the game client know it should move when I only send it to server and receive a response? Does the client upon receiving that info from server move or? If anyone has any idea on how exactly this part works I'd appreciate the input. Thanks!

Depends on the game. If the movement is synced in some manner after you send the packet to move, the server will respond back that it did or didn't move etc. If the game doesn't sync then if you want to visually see the move you'd have to tell the client to move by force as well.