Scarf Yveltal isn't a wallbreaker -- it's a revenge killer. Marshadow & Gengar-Mega are more of breakers than revenge killers (though Gengar-M can be labelled as both) and do a totally different job than Scarf Yveltal. For more on Yveltal, you can check out one of my Smogon VR posts (scroll to the bottom of the post for Scarf Yveltal):
https://www.smogon.com/forums/threads/anything-goes-old-gens-hub.3663615/#post-9053351 (Love react it if you ever get the chance lol)
CM Groundy + Ray-M + Kyogre-P is a classic core. Good luck!!
