eevee-s rly supports mgyara by 1 providing a secondary check to m-gengar, with glitzy glow + sappy seed eevee actually walls any mgengar set without sludge bomb, which are the sets most likely to trouble mgyara. 2 mgyara tends to be overworked, wanting to check gar/(zam)/offensive mew/starmie & also wanting to be able to take a hit vs melmetal, aero, maybe even vs zapdos in some cases so it rly benefits from rest.
rest mgyara + rest melm together check most of the tier and cover each other somewhat tho they share the fighting weakness and struggle w zapdos.
~ gyara spreads para rly well due to zapdos being the only plausible twave immune switchin and its bulk, and the whole team rly values para. twave can be a good move to select right before using rest and also can increase chances to rest loop bc of full paralysis. dropping eq mainly affects vs melmetal as twave is better for a poliwrath switchin anyway.
adamant is an option to improve melmetal matchup and hit zapdos harder on the switch but careful is more consistent for the teams primary special tank.
~ melmetal running ice punch is to enable it to pressure zapdos better either on the switch or staying in on zapdos, to pressure it to actually click thunderbolt (or roost) and not j u turn out of a predicted rhydon switchin. rhydon rly doesnt want to switch in to u turn bc its so easily forced out and is the one poke on the team that can rly lose momentum. twave is possible in that slot, but it is basically unusable if opponent has zapdos, and mgyara should be better at landing para on poliwrath anyway and starmie isnt a big threat bc of mgyara.
~ as stated eevee-s runs glitzy glow esp to be able to check non sludge bomb mgar. mgar is the primary target of buzzy buzz anyway and can block it with substitute, and glitzy glow much better protects eevee's health to be able to swirl in addition to being more consistent v mgar. on this team eevee-s rly does not want to spam sizzly slide too much, it is more for physical attackers that may try to switch in that it would lose too much momentum to switch out of such as mgyara and potentially poliwrath.
~ gengar is chosen for a secondary mega (basically only will mega for m-bee teams). against m-bee teams it provides an offensive check to mew, since u dont have mgyara to check it (and obv is a generally threatening mega). otherwise / in base form, it provides a second switch in to poliwrath (or hitmonlee etc) alongside mew, is still a strong offensive threat esp with possible para support from mgyara, and provides a fast wisp if needed. it also has an ok matchup w zapdos and can even switch in to anything other than thunderbolt (which zapdos may not want to click as long as rhydon is healthy). mega drain is listed here as second attack as a pretty spammable attack after switching into poliwrath, but thunderbolt is definitely better against m-bee teams where mega drain is not spammable and where gar is most important due to being the teams mega in that matchup so the choice depends on hm u want to prioritize m-bee matchup.
(aero would not rly fit well on this team due to not switching into either zapdos or poliwrath well.)
~ rhydon is a zapdos and m-bee check and generally a strong bulky poke that loves mgyara's para support particularly on poliwrath. megahorn is run over toxic bc there is eevee s support to heal burn and toxic doesnt fit the teams playstyle well as para or burn is always preferred (except against zapdos, which there is no way for rhydon to hit with toxic anyway). eg toxic on mew actually does not rly help this team bc it protects mew from para which allows it to burn mgyara. the megahorn damage is much more useful to put in in range of gengars shadow ball or burned mgyara's crunch.
rhydon's biggest issue is u turns from the pokes it is supposed to check, so try to use the teams u turn resists (melmetal, base form gengar for zapdos, base form gyara for m-beedrill) to deter u turn and allow rhydon to come in on a different move (and if u mispredict and lose a poke that was trying to switch in on u turn, then at least u can bring in rhydon right after and set rocks or attack which rly isnt so bad). so keep in mind that u may not want to bring in rhydon on zapdos or m-beedrill if u predict u turn.
~ mew needs to have psychic to threaten poliwrath / to some extent other fighting types that 4/6 of the team is weak to and that it is switching into often. an offensive set makes most sense to have the best chance of gaining an advantage whenever mew switches into poliwrath, and since psychic is required that leaves nasty plot as the best set. if gengar can burn a-muk/mgyara for mew then mew can be rly hard to defensively check after that, but if not a-muk is easy for this team to switch into anyway (obv mgyara, but also melm and even eevee-s can switch in esp to coverage moves tho theres no reason to if mgyara is healthy). being offensively checked by mgar is less of a concern since the team has eevee+mgyara to together check all mgar sets, and since if mgar tries to use a coverage move to catch the switchin but mew stays in its game over that makes it much safer to bring eevee or mgyara in directly.
outside of the m-bee matchup (and to a lesser extent m-pinsir), nasty plot mew is very threatening and this team deals very well with most of its counterplay.
roost is primarily to be able to continue setting up vs burned a-muk, and also to later heal toxic damage if the status was able to be removed by swirl. but this team wants to play mew v 'aggressively' so it will mainly be either setting up or attacking. therefore dropping roost and instead st like nasty plot, fire blast, mega drain, psychic is possible.