Zangoose is unfortunately outclassed in the OU metagame by other physical breakers. In fact, the Mimikyu on your team will pretty much perform the same role as Zangoose (besides the ability to pressure steel types with Close Combat, but you already have Charizard-Y to pressure them) but better. Registeel too is outclassed by other defensive steel types in the metagame such as defensive Heatran and Assault Vest Magearna. You're better off replacing Zangoose and Registeel with more viable pokemon that support your team. Thunder Wave Ferrothorn might be a good replacement for Registeel since it can also take on Greninja and set up hazards while being able to spread paralysis as well, which helps out Mimikyu and Charizard-Y a lot since their speed isn't that great. Here's a set that will probably work for your team:
Ferrothorn @ Leftovers
Ability: Iron Barbs
EVs: 252 HP / 24 Def / 232 SpD
Careful Nature
- Stealth Rock
- Leech Seed
- Thunder Wave
- Power Whip
Also, you might want to run Explosion over Knock Off on Landorus-Therian to have another way of revenge killing Hawlucha since your answers for +2 Hawlucha are pretty shaky. Charizard-Y is guaranteed to live a hit from full health and Rotom-Wash only has a 12.5% chance to get OHKO'd, but Rotom-Wash can very easily get chipped into range of a +2 High Jump Kick. Especially because it's your main defogger so you're likely to be switching it into hazards over the course of the match. Mimikyu can use its Disguise ability to take a hit and kill it with Play Rough, but that greatly hinders its ability to set up in the late game, so it's not particularly desirable to be put in that position. I don't really see a good way of fitting a reliable Hawlucha check on the defensive side on your team, so it'll help out the matchup versus Hawlucha more since you'll have another answer to it. Granted, Hawlucha can only set up on Ferrothorn and with Thunder Wave on it, you can cripple it with Paralysis as it sets up so it's not really a "free" setup either. If you feel like you can handle Hawlucha fine with just those methods that I mentioned, then you can keep Knock Off since the ability to remove Leftovers from defensive pokemon is pretty useful for your main breakers.
Not really sure what you'd need as the 6th pokemon to replace Zangoose, though, unfortunately. I'm noticing that there aren't really any good ways of taking on Toxapex with the team so far. It walls Charizard-Y and can take a +2 Never-Ending Nightmare from full health and Recover off the damage, after which it can just Haze your boost away. Landorus-Therian can take it on, but it doesn't want to risk Scald burns. Something that can reliably take on Toxapex as your 6th pokemon would make sense.
One last thing I'll suggest is a few changes to the EV spreads on some pokemon. First of all, Rotom-Wash is mainly used as a defensive pivot and hazard remover, so the EVs in Special Attack are unnecessary. They're better off being thrown into Defense to improve its bulk and defensiveness. I'd recommend the standard Smogon spread of 252 HP / 200 Def / 56 Spe with a Bold nature. This spread runs enough speed to outspeed Adamant max speed Tyranitar with the rest of the EVs in its defensive stats. You should also replace Pain Split with Will-O-Wisp because even though getting health back through Pain Split can be useful, being able to burn physical attackers and defensive pokemon is more useful here, in my opinion. For the Landorus-Therian spread, I'd also recommend the Smogon spread of 232 Atk / 68 Def / 208 Spe. This allows it to outspeed Kommo-O at +1 Speed and be able to live an Acrobatics from Hawlucha after Stealth Rock damage. Finally, Charizard-Y should have its 4 HP EVs moved to Defense so it can have an odd HP number, which allows it to take Stealth Rock damage one extra time without getting knocked out. Also, I'd change its nature to Timid since the extra speed is useful for outspeeding a few pokemon like Kyurem-Black and non-scarf Tapu Lele.
Hopefully this is fine for a rate! I know this isn't quite a full team rate, which made me want to leave it as a comment, but it's too in-depth and lengthy to leave as a comment.
Here's an importable of the 5 pokemon after the changes so you can copy/paste it into the Showdown teambuilder whenever you choose to work on finding a good 6th pokemon.
