I took a look again at all the hoen pokes and most of them seemst
just ripe for a mega evolution, so here are my thaughts, also these are not full one builds for pokes:
1. Mega clamperl lines (gorebyss/huntail) one for each version just because we get 2 games
both in increase in their best stats and speed or health
2. Mega walrein not that much needed but everyone loves/uses him and could become either bulkier(defence), or faster to make him a tank
3. Mega Milotic (because feebass atrocity) would seem pretty cool and is also used by the last gymleader
4. Mega snorunt line (Glalie/Frostlass) just one but he seems pretty cool to have a mega with more special attack and inbuild hail
5. Mega castform, this way he would be more used and also a ability which lets him change weather every turn random or
whenever someone uses a weather move it changes to something random
6. Mega wailord (release the kracken) this would be well suited with the regi pussles because come on a normal wailord could have trashed the place years ago but no
7. Mega Exploud just make it even more powerfull + ability makes sound moves 1.5/2 times stronger
8. Mega Breloom change to like something not 4x weak + everyone captures this so wy not
9. Mega Swellow because everyone would like it