So I have a bunch of things to say..... I won't say your team is bad, but first of all, rotom-frost is NOT a physical attacker, it also should not have trick, it is defensive and leftovers is good for it. I recommend that you replace trick with nasty plot/volt switch and move the attack boost to special attack. ONLY if you chose nasty plot, then keep substitute, and if not, maybe give it hex.
I have some things to say about Umbreon too. Umbreon is also mostly a special move learner and dark pulse is better than snarl or bite, so replace psychic with dark pulse. You should also replace moon light with wish, it helps yo in circumstances where your worried about health a few turns later. Change detect with protect because it is overall better. And lastly, I recommend changing confuse ray to toxic, Umbreon is a toxic staller mostly...
Great idea with belly drum! But instead of shadow ball have shadow sneak, which does 160 damage with stat boosts, and instead of trick have play rough, because fairy is the new best type. Wood hammer... Meh... I don't recommend it because it is a recoil move and is overall, not so good on Mimikyu. Instead, I would chose destiny bond, for late game bangers.
Nice name! But give it an Gengarite... if it's national dex. Also replace sucker punch with destiny bond, sucker punch is just dumb on Gengar. But now for the iv's, put them all into special attack and speed, gengar is meant to be a fast sweeper. Also replace the black sludge because Gengar would die in one shot so no point of any multi turn healing items.
Its actually... your best one. All the moves are good, but give it a choice scarf and modest nature, that would make it a huge sweepy boi. Also, dont invest into attack! Invest into special attack for Vikavolt.
For Spiritomb, invest into HP and special defense, since the only type that beats him, is usually a specially attacking type. Also for it to be an avid toxic staller, you should give it pain split instead of shadow ball, because poltergiest fills in. And don't give it a hasty nature, it is a toxic staller, so give it a sassy nature.
Something I want to clarify
Some of your mons don't have natures so i will list them out:
I know this was really long, but long story short, you need to fix your team. Hope you win a bunch of battles with your improved team, and I hope I helped you! Bye!