so mega-manetric was what was requested, yet again i recomend at least trying out with mega diancie+thundurs instead, at least to compare. the set is what you gave, but i've found the 40 hp not particularly helpful, thus removed them. the relevant threats 396 hits beats as you said mega gengar, and things like mega aerodactyl, +1 blaziken, etc.. but i've just found them way too uncommon to prepare for, and mostly lose power just to beat. i wanted at first to use it like raichu, on certain teams, with gyarados and such, but helping water types made me take a rain route, and rain gave me the thunder instead of volt switch idea. politoed is a rain setter, physically bulky to stand up to kangaskhan and scald, and to hold hands with pokemon and giving them moral. ice beam is for certain mushrooms (amoonguss) and thundurus mostly. kingdra was chosen over ludicolo because i like the spread, deals with kyurem black, and is overall more scary to be facing, in my opinion, plus dragon is a solid type. talonflame is your "fire in the rain" as ferrothorn, amoonguss, mega venusaur are horrid to face (overheat on manetric has merits here i suppose). i gave it will-o-wisp to annoy kangaskhan, particularly, since the team's direct way of dealing with it is terrakion, who doesnt like losing its sash on a switch in. jirachi is a spore check, a very bizzare second rain setter whom
checkmater75 inspired me to use in his archetype. redirection is also kinda useful i suppose. the steel typing is the biggest benefit it gives tho, in my opinion. terrakion is your second sun check, kangaskhan check, fast fighting type, and carries taunt for trick room, plus sash. what you can do is swap taunt between terrakion and talonflame, giving the other quick guard, as both learn these moves, helps a lot with thundurus, blocking thunderwaves and taunts, which you want. or you can keep will-o-wisp if you're a mega kangaskhan phobic like me, but do keep quick guard in mind, it helps the team so much. additional tips would be considering lum kingdra, eject button politoed, and to an extent life orb terrakion, but that last one is too shaky.