Happened to build this team because Celesteela is just such a dope Pokemon to play with, honestly. Was not sure where to start, but I decided to go with Mega Pinsir as suggested on
this post by AM. Steela and M-Pins are quite effective at wearing down teams for each other, which is pretty dope. Next thing was looking for a spiker, and Greninja seemed to be a good fit. Standard fare for offensive Spikes, from what I can tell. Gunk Shot chunks Tapu Fini to dissuade it from defogging, Ice Beam hits Lando and Chomp, and Hydro Pump is just strong. EV spread guarantees the KO on Tapu Fini with Gunk Shot provided it switches into Hydro Pump after rocks. From here I went for Special Pheromosa as my spinner. I used to run Physical, but went to special as suggested by Colonel M in order to avoid using HJK / Rocky Helmet recoil. I previously had Focus Sash Dugtrio, but I kept having a few problems with Tapu Koko and Volcarona. So instead, I decided to sacrifice any sort of chivalry and respect towards my opponent and run Scarf Dugtrio to trap my aforementioned threats. Edgequake is good coverage, Memento helps steela / m-pins set up a tad easier, and Aerial Ace hits Pheromosa the hardest. Since I've apparently dug a hole deep enough with teambuilding, I happened to notice I kinda just lose to Ash-Greninja (plus I didn't have rocks since doug was scarf). So after trying stuff like Colbur Berry Jirachi, Ferrothorn, and even specially defensive Cradily at one point (wish that worked, honestly), I settled with a motherfucking Chansey. It's honestly just there to sponge special hits from stuff like Tapu Koko and the like provided I misplay with Dugtrio. Rocks / Soft-Boiled / Stoss is standard Chansey stuff, and Healing Wish is pretty cool if I happen to be in a match-up where I require to heal up one of my mates more than keeping Chansey alive).