Might I ask for some suggestions? I'm trying to plan out a try-hard team for this generation, but since there aren't full 'mon specific analysis' yet for the new generation to go off of, I've got some gaps that I dunno what to fill with.
The three that I want to use for absolute certain are:
Mega Beedrill (I know it's not available yet, but can still plan for it), Dhelmise (Favorite new addition, as well as a good Spinner partner), and Mimikyu (Other new favorite, and surprisingly good fighter with SD Disguise shenanigans).
Strongly considering Toxapex as a 4th, but would still be willing to concede it if there would be something better in its spot for the overall team comp.
Only limit I ask is that the 'mons in question have to be breed-able, since I'm a cartridge player instead of a Showdown player (so no Legendaries/UBs).
It seems there are a few gaps in your team. Firstly, all three mons are special attackers. Secondly, both Dhelmise and Mimikyu struggle against Ghost-Type opponents. Thirdly, Dhelmise and Beedrill struggle with most fire types. Fourthly, all three have trouble attacking steel types.
Rotom-Heat works as a special attacker to counter steel types, as well as a bulky pivot with Volt-Switch and Levitate to counter ground types. Its well rounded stats and few weaknesses allow it to play a variety of roles, as well as a few good support moves (Thunder Wave, Will-O-Wisp, Pain Split, Trick) Give it Leftovers to enhance it's bulk, or Choice Specs for high firepower/Trick shenanigans.
Since Lycanrock would kill most of your team so far, perhaps add a counter to rock types. Lucario has good Special Attack and Speed, and can KO the rock types that threaten Beedrill and Rotom, as well as the dark types that threaten Dhelmise, and even ghost types with Dark Pulse. I would run a special set to defeat physical walls, and maybe even Vacuum Wave for priority. Life Orb gives it a good bit more firepower, as well as versatility with moves.
Fire and ground types have been a threat thus far, so a good bulky water type would be useful. Toxapex can be a good pivot with it's bulk and Regenerator, though it would struggle with Ground types. Gyarados has solid bulk with Intimidate, as well as good offense and the ability to use Dragon Dance. It's weaknesses are generally covered by the other teammates, and with Earthquake provides a wealth of valuable coverage. Item wise, a healing berry would help set up, though none of your teamates have Z-Crystals yet. Perhaps give one to Gyrados for a one-time nuke/powerfull coverage move?
I'm not an expert, but I hope this helps a little. If you want to build around Toxapex, you might want to swap out Lucario for something else.