My Magcargo has this moveset, and it is amazing what this moveset does for me.
Item-Currently, Macho Brace;Still training him.
Shell Smash-Makes him surprisingly powerful when used
Rock Slide-More STAB, but looking for a better move...
Recover-For when you're in a pinch
Try out this moveset. It's fun!
P.S. My Magcargo's main reason that he's so good is that he started out as a Lv. 1 Schneckmag (German Slugma) and I trained him a bunch to get him to Level 52. So, it is highly suggested to get him from an egg, so he can get better stats. Just sayin'.