(even if you aren't vegan)
The idea of Team Attacks, to me, stems from an idea in WUW D&D.
Barty Tumblebelly, a character belonging to someone else, was supposed to do more Team Attacks with other PCs in referandum to the Mario & Luigi Superstars Saga. It didn't come up often for others, but I out-of-character thought it was a good idea to do. As such, my Neutral-leaning-Neutral-Evil Druid, Eozerus Largo'thog Ikezawa-Lelouch, wound up bonding with a genuinely Good (I think he was Neutral Good?) Dwarf Fighter through usage of attacks that synergized with the specialties of both their respective classes. Even Ezzie herself was not necessarily always able to partake in Team Attacks with Barty all the time, though, and when I left WUWD&D I don't think she and Barty did any more Team Attacks (unless the GM - Chaos - hasn't told me about them).
Occasionally, Wikihood has acknowledged that WUWD&D (nicknamed "Golgotha+, Golgotha++, & corresponding tabletop spinoffs") exists as a legitimate alternate universe, in some forme. Madelyn Raid, Remolay's character, has effectively been a mainstay of most of his universes - as such, when Leigh was remade, Maddie came with him. Instead of becoming the Cockpuncher, however, Maddie was made into a normal girl. There was also a Volkov Ring, which was a moderately useful magical item in Golgotha+; also, the concept of Quickwood was something Wikihood had intended to weaponize for its own universe, but quickly became the material necessary for The Clock King to be able to remake a different character (Talos) into a Hexblade from his original Paladin/Warlock mix.
Lex teams up frequently with other people - Chaos in the San Cristobal Casino Heist of 2015, Garfield and Volkov in various misadventures throughout the three-year prison sentence Chaos underwent, and Noelle when Chaos needed to be rescued from the DuTempis. I operate under the assumption that Lex has done at least one Team Attack with Chaos, evidenced by how Lex and Noelle synergize their attacks so easily with each other in spite of not having known each other for very long (Noelle is also a masterful fighter, having won many Battel Tournaments in the past - especially the 2016 Women's Strawweight; as both Lex and Noelle are experts, it can be assumed it didn't need to take very long for them to co-ordinate into a Team Attack compared to Lex's interactions with other ally characters).
Garfield has likely also partaken in Team Attacks himself, to a lesser extent; but, he would have only done so with Lex, Volkov, or Stephanie. His pool of allies that are proficient in combat is far more narrow than Lex's. A Team Attack between him and Volkov almost happened, but Rosemary Touchdown fights are normally intended to be 1v1 showdowns in the first place. On top of that, the Rosemary II fight had to be downscaled to be less Fire Wall-intensive / explosive, and so was ended in "most effective tactic available" fashion. Likewise, Volkov's main fight also had to be downscaled so - instead of fighting a major loa like Baron Samedi - Volkov instead fought a minor Pytreaux loa (Wikihood universe's Petro loas, which are of the Fire element and thus weak to an Ice weapon in Volkov's immediate possession).
Team Attacks are liable to happen in the future, since conflicts will probably get more powerful as the series goes on.