[HELP] Breeding Seismic Toss Chansey

[RetroTyphlosion]

Hey guys,

I've been trying to breed a Seismic Toss Chansey for a while now. I got my Mankey (with Seismic Toss) and bred it with a Mawile. However, all the Mawiles I'm hatching don't have Seismic Toss, and its getting really frustrating. Does anyone know what I could possibly be doing wrong?

Thanks,
Retro