want a few mons unranked like right now.
rotom-h: rotom-h's niche is long gone. it handled genesect and mawile, those are banned. the main issue is just that it's outclassed by rotom-w. it does boast a neat pool of resistances (to electric and grass which rotom-w lacks), allowing it to check a few different threats, but it becomes weak to rock and water. this means it's weak to rocks, which destroys its abilities as a pivot and means it can't deal with cb talonflame consistently enough, it can't beat azumarill, it can't beat landorus-t, it can't beat sand excadrill... it's pretty much impossible to justify rotom-h on a team because despite having a different pool of resistances/weaknesses, rotom-w or a better defensive fire-type such as heatran is pretty much always infinitely better. completely outclassed, practically no reason to use on an ou team, unranked.
hydreigon: this pokemon is just shit which aegislash gone. the whole point was an aegislash check as well as a nice way of checking mega mawile with lo fire blast and not being koed by +2 sucker punch, but that niche is gone. pretty much the reason that it's unviable is just how good the latis are. hydreigon is slow, too slow. hydreigon doesn't have the defensive typing to beat land or keld or zard y, or really much of anything. it's screwed by clefable even more, and screwed by av azumarill much more. sure it can 'wall/stallbreak' except for the fact that clefable exists (the steel moves are shitty options). it doesn't defog, it doesn't healing wish, it doesn't do any of that. it's just a pretty good wallbreaker, and one fucked up by clefable at that, in a metagame where the latis are ridiculously dominant. completely eclipsed, unranked.
diancie: i really hope i don't have to explain why this terrible, the only reason to use it is as a dumb tr lead which isn't enough to rank it, lol.
umbreon: garbage. it gives free switch-ins to terrakion and keldeo, nice. it's passive as shit, it's fucked up by fairies, it doesn't really wall that much...need i really say more? no one uses this on a serious ou team, unranked.
zygarde: this pokemon is terrible. it's supposed to sweep but when is it sweeping any competent team? never. almost dead weight against offense because although it can tank some hits, it's too weak to do much back, dead weight against pretty much every team with a clefable too and fucked by fairies in general. zygarde is outclassed and has a complete inability to sweep competently in the ou metagame. unranked.