7th Gen Taking on the Battle Tree for the first time...!

[I will be talking about building competitive Pokémon in this thread but I didn't put this in the competitive forum because I'm only talking about the Battle Tree... I hope this is in the right section]

I'm trying to get through the Battle Tree in Moon because a) I want the Venusaurite and b) I want to try and get competitive good - I've been learning about EVs and IVs, more strategic play etc - and so I have built up a team for the Singles. I tried one match and beat a hiker, but then I got totally wrecked by a girl using psychic Pokémon haha...

The team I've built, currently around lvl 75 (I know levels go down to 50, but I'm trying to build up to lvl100 to max out stats - if I am understanding correctly how the EVs/IVs work) is as follows:

Clefable F. [Bold, Magic Guard]
IVs: HP (best), Att. (best), Def. (best), Sp. Att. (best), Sp. Def (decent), Speed (best)
EVs: 252 HP, 252 Def, 6 Sp. Att.
Current Moveset: Lucky Charm, Minimize, Moonblast, Return

Bewear F. [Adamant, Fluffy]
IVs: HP (best), Att. (best), Def. (best), Sp. Att. (best), Sp. Def (fantastic), Speed (best)
EVs: 252 HP, 252 Att., 6 Def.
Current Moveset: Swords Dance, Brick Break, Earthquake, Return

Mimikyu F. [Jolly, Disguise]
IVs: HP (best), Att. (pretty good), Def. (best), Sp. Att. (best), Sp. Def (best), Speed (best)
EVs: 252 Speed, 252 Att., 6 Def
Current Moveset: Swords Dance, Shadow Claw, Play Rough, Thunderbolt

I have a Timid/Snow Warning Alolan Ninetales and Quirky/Chlorophyll Venusaur in reserves too. Both have really good IVs.

I was just wondering if you guys could evaluate my team, and give me any tips for the Battle Tree? I really wanna get good!!

That seems like a solid team for Battle Tree.

For Clefable give her a Life Orb which you can find in Resolution Cave. The Nature and IVs seem fine but maybe swap Minimise for Calm Mind (TM) which will boost both your special attack and special defense.

Clefable's attack stat is less than it's special attack and Bold Nature reduces the attack. Maybe swap Return for Psychic (TM) which will hit any Poison types you come up against. Lucky Chant is nice to stop crits ruining things but Thunder Wave could work here too as the team is other than Mimikyu quite slow.

Mimikyu's special attack stat is lower than its attack so maybe change Thunderbolt to Wood Hammer. (Move Relearner) and give it the Fairium Z.

Bewear looks fine but I have never used one so I'm not sure what to suggest.

In my experience the Tapus work very well in the Battle Tree especially Tapu Fini. Kartana is great too if you can get one especially if it is Jolly.

Megas do not appear in the Normal Battle Tree although Red may use a Mega Blastoise in Battle 20.

Getting to level 100 is not necessary for either Battle Tree or Battle Spot. Once you hit level 50, you're good to go, unless you need to level up further for evolution, level-up moves, or wish to Hyper Train a Pokemon. Especially since leveling up to 100 is more work than it needs to be in Gen 7.

That Clefable set could use some work though. Return is very weak on something like Clefable. Minimize is a double-edged sword in that while you can hax wins out, the same can also happen to you--it's not going to 100% guarantee misses, so you'll eventually get hit by something, or the game will just throw stuff at you to nullify or ignore the evasion boosts. And if you're looking to get into competitive, evasion altering things are outright banned in some (but not all) formats, and are immensely frowned upon in general.

Shadow Sneak is also nice on Mimikyu.

Something to keep in mind about the Battle Tree is that it may take a few tries to get that 50-win streak. It's kind of impossible to prepare for everything, yet you have to deal with a lot of shit while also never once losing.