This core lends itself more or less exclusively to hard Trick Room so that's how I decided to build it; the inherent redundancy between Mawile and Stakataka meant that the remaining three slots needed to be as diverse as possible to to cover typings and threats. With that said, my first new addition to the team was chosen to support the two Steel-type attackers and provide a sturdy all-purpose bulky attacker for the team: AV Tapu Bulu. This Pokémon was chosen to take care of bulky Waters such as Tapu Fini and Suicune, and to buffer against Earthquakes with Grassy Terrain. It has some utility in answering certain Ground- and Dragon-types, and in nuking bulkier opponents with Wood Hammer, but is mainly here for type synergy purposes. The fifth slot is an interesting pick - I went with Focus Sash Nihilego to help curb the rising issue of attackers such as Volcarona, Mega Salamence, Tapu Lele, and Mega Charizard Y, and to give the team some level of speed for matchups where consistently setting Trick Room could turn out to be unlikely. Nihilego has Trick Room itself as a tech option in the fourth slot; this allows for the possibility of setting a suicide Trick Room for one of the slow breakers, or catching an opponent offguard, or for playing with speed tiers and getting the jump on faster threats such as Tapu Koko, Mega Salamence, Mega Gengar or Naganadel. I played with a number of different Hidden Power types as I navigated my matchups with problem Pokémon such as Ferrothorn, Heatran and Celesteela, but eventually settled on Hidden Power [Ice] to check Naganadel and Landorus-T. Lastly, I chose Araquanid as a reliable resist to the team's Fire-, Fighting-, Water-, and Ground-type weaknesses, as well as as a multi-purpose stallbreaker, one-time nuke and anti-gimmick tool. Soak+Toxic allows Araquanid to play mindgames with Pokémon such as Ferrothorn and Toxapex that come in to soak up Hydro Vortex. Offensively, Araquanid is very one-note so it has the moveslots to spare. At this point, I was having issues with Cresselia's passiveness and with the overall matchup with Steel-types - Mawile was running a Substitute+Focus Punch set but it was struggling to consistently beat Celesteela so I first tried SD Thunder Punch, and then moved on to Fire Fang to catch Ferrothorn as well. Cresselia dropped Ice Beam and Moonlight for Psychic and Toxic, to cover more ground with neutral damage and ensure that it could have a lasting impact on the game even if the opponent brought an Ice resist. Stakataka is a Defense booster with a standard OTR set and Life Orb, to ensure that it can boost to take hits from Landorus-T and also 1v1 Aegislash with Earthquake. That's all I really have to say about this team overall so Merry Christmas Feesh Squad! I hope that this squad is similar to what you were imagining <3
here's a really average replay bc i didn't test for long enough to get really good ones rip
https://replay.pokemonshowdown.com/gen7battlespotsingles-673492591