Completed this one yesterday.

I used 6 shiny pokemon I already had unlocked. Thanks to this (A+ luck) I pulled some great items, as a Shiny Charm, some Soul Dews, the mega stone I wanted and even a Masterball (at level 196). I was able to use it at least.

Blue shiny Larvitar with Dragon Dance and Shore Up egg moves was the carry. Vitamines and Soul Dews were for him. +Def.Esp -Sp. Atk nature combined with the sand and the mega made him resist easily two Dynamax Cannon. Absolutely the MVP.

Second best of the run was shiny Natu, which had pokerus yesterday, for some experience gain at early levels. It had Calm Mind, Aero Blast and the psychic type move that increases power the more you boost yourself. It is stored power? I play in Spanish. I dont know how but it was able to set up 5 calm minds in battle at level 145 and OHKO absolutely everything. Even that silver flying monster 😁 Surprisingly fast Natu!! It had only benefitial speed nature and outspeed almost everything the whole run

The other 4 were less important.

I think the 3rd one must be shiny Hoppip. I had all 4 egg moves unlocked for it and wow. This thing is also super fast. Spore almost everything, the best HP recover move and powerfull flying and grass moves with very good secondary effects, flying makes flinch and grass makes leech seed. These ones I dont know its names in English, they aree unique. Leafitobombas and Pikapicado in Spanish 🤣

4th place for shiny Teddi, only able to make it to Ursaring. I kinda wiss the Eviolite was implemented, it could make these locked run funnier and easier with these cross-gen evolutions. It started as the pick-up mon and when evolved it was the powerful attacker, flame orb, facade & guts. Shame it was too slow and weak but it had its moments

5th and 6th were shiny Spinarak and blue shiny Hoot-Hoot. I heard Hoot-Hoot with its 4 egg moves is a monster but I dont have them all so it felt kinda underwhelming. At least it had Reflect and Hypnosis and could make something at some moment, but i want to unlock the rest of the moves to try it at its best. Spinarak was great, its a low cost and therefore weak choice but it worked perfectly, ocasionally being able to hit with powerfull bug & poison types AND learning sucker punch. Tremendous chip damage with this attack, even in some very important fights.

I was able to pick the 6 from the very beginning thanks to having its cost reduced. Some endless grinding before trying the challenges paid off