berry with Intimidate Corviknight
The Number Man with Galvanize Kommo-o
Quantum Tesseract with Water Absorb Gengar
Atha with Water Absorb Excadrill
Completely Incognito with Sheer Force Cloyster
Thinkerino with Dragon's Maw Naganadel
Flaming Deoxys with Primordial Sea Zapdos
drampa's grandpa with Magic Bounce Slowbro
So since we have such a strong list of options that my answer isn't immediately obvious, I think it's worth giving some explanation rather than just dropping my answers. After eliminating my own submission, the things I prioritize were:
1. How much does it help weavile in the match?
2. How much does it help weavile in specific, rather than being a generic teamate for offensive pokemon?
3. How creative is it?
Intimidate Corviknight: It covers triage, physical scarfers, and entry hazards. It can bring weavile in safely to do its work, albeit without the ability to pressure in Pokemon that Weavile likes to take advantage of. It's not really something for weavile in specific, but Hurricane Corviknight is still fire as fuck.
Galvanize Kommo-O covers water-type attackers for Weavile; although it doesn't switch into them, it has the advantage of them switching in to it. It's specifically focused on luring the Pokemon that Weavile needs gone, rather than incidentally KOing them, so it gets points there. It's also a fairly unorthodox pick.
Water Absorb Sand Tomb Excadrill struggles a lot with having weak initial power and mono ground-type offense, but in terms of supporting weavile that's less of a big deal, as it can still do its job of eating attacks from some of Weavile's biggest nuisances and forcing them out - most notably doing so for Fini, as unlike most setup sweepers Fini can't safely stay in on it a bit to fish before going out to a hard counter due to Sand Tomb. it can also Toxic most non-Corviknight flyers, and since a lot of them can't do much to it, that lets Excadrill sit in on them until they're forced to switch out, which means they're much less of a stop to Excadrill than they could be. It can block flip turn outright, which is super abnoxious for a lot of teams, and hard walls Barraskewdas that choose Psychic Fangs coverage, which is great for offenses and balances that carry Weavile. It's also not something I have ever seen before.
Smash Cloyster is a cool mon in general, major points for that, but as an offensive partner it struggling so much with Toxapex, Suicune, and Golisopod don't do it any real favors. It needing to set up to do that job is also a minor point against it.
Thinkerino gets a lot of utility points for one of the best mons in the metagame, but it doesn't do that much for Weavile in specific, or vice versa. Neither Weavile nor Naganadel really have chances to switch into each others answers directly, nor does either have a pivot move, which requires them to make use of a third party pivot which is significantly worse at gaining momentum from unshared checks. In turn, yes, weavile can remove items from Zapdos' checks, but only if they stay in, and this core has no way to punish them if they don't play along, which is a major point against it.
Flaming Deoxys does offer a set to force out some of Weavile's checks, but like Naganadel it doesn't love switching in to them. However, unlike Nagandel it can pivot and has recovery, two huge factors that make Zapdos a much better teammate at getting Weavile in. While it doesn't love switchin in on Weavile's main checks, it can do so, and on lesser checks like Choice Scarf Victini it has a much easier time. It's not entirely as good at
removing checks to Weavile in the way some of the lures are, though, since it announces. It's not rare per se but it is cool so I'll credit it there.
Bounce Slowbro keeps rocks off, but only if it can answer the rocker. Slow teleport is nice for bringing Weavile in, but it doesn't do so on things Weavile beats like Zapdos does and doesn't do as good a job checking water-types as Excadrill does. Future Sight is a nice utility for helping Weavile break past walls, though, which earns it back some points. Ordinarily this would probably make my list but the competition is stiff enough that it's not top 3 submissions imo.
1. Atha
2. Flaming Deoxys
3. The Number Man