Is it Adamant or Jolly? 252/252 is not always optimal, but you can run it with a Jolly nature if you want to outspeed non-maxed speed M-Kangs.
The common moveset is:
Fake Out
Sucker Punch
PowerUp Punch
Return/Double Edge
Howewer, this moveset can change if you have particular requirements:
Do you have at least one pokemon who can manage to kill another M-Kangaskhan? If not, replace PowerUp Punch for Low Kick to deal with opponent's M-Kangs.
Do you have a faster Fake Out user in your team? Then you could replace Fake Out for Protect.
Do you have a support pokemon who can redirect attacks? Then you can run Double-Edge over Return and accept the risk of recoil.
If your team lacks Ground coverage you shouldn't sacrifice a slot on your M-Kang, but find an alternative (such as to add a new pokemon)
Drain Punch is an option if your anwser to the first question is Yes and you are running Double-Edge too.
The common moveset is:
Fake Out
Sucker Punch
PowerUp Punch
Return/Double Edge
Howewer, this moveset can change if you have particular requirements:
Do you have at least one pokemon who can manage to kill another M-Kangaskhan? If not, replace PowerUp Punch for Low Kick to deal with opponent's M-Kangs.
Do you have a faster Fake Out user in your team? Then you could replace Fake Out for Protect.
Do you have a support pokemon who can redirect attacks? Then you can run Double-Edge over Return and accept the risk of recoil.
If your team lacks Ground coverage you shouldn't sacrifice a slot on your M-Kang, but find an alternative (such as to add a new pokemon)
Drain Punch is an option if your anwser to the first question is Yes and you are running Double-Edge too.