Always more to find
A wild level 60 Chansey with a Defense IV of 3 or less always has a chance of being OHKOed by any Shell Side Arm coming off 110 or more Attack. If you have no way of verifying what stats the Chansey has (such as by catching it after hitting it), then the test doesn't mean much. The Wooper I saved in front of to do my several dozen tests happened to have a Defense IV of 0 or 1, so it's not unheard of. Anyway, said tests that I posted on the last page already prove it only ever calculates Attack with Defense or Special Attack with Special Defense; there's no mixing or Wooper would be taking over 100 damage every hit in the 168 Attack, 141 Special Attack series of tests (which, if mixed would calculate Attack into Special Defense).From my perspective, this move is extremely smart. It seems to be using Galarian Slowbro's highest attacking stat, whether it's from its Attack or Special Attack stats, and translates that higher stat number to either physical or special damage depending on which defensive stat from the opponent is the lesser of the two. It's like a much better version of Photon Geyser that adapts to the situation at hand. I'd also like to see more people test this out to see what they think about all this.
More Shell Side Arm stuff:
Additional testing shows Reflect does nothing to Shell Side Arm's decision-making. A 106 Defense, 126 Sp. Def opponent continues taking physical Shell Side Arms (from the 141/141 Slowbro) every turn after Reflect goes up. So, the only explanation that makes sense for the Reflect Gardevoir video from earlier in the thread is that its Defense and Special Defense were somehow the perfect combination to take identical damage rolls from both categories.
Since Choice Band doesn't affect this move's category, I strongly doubt any item or Ability does (in the same way that Photon Geyser doesn't care about non-stat stage boosts). I don't have anything with Ice Scales at the moment so someone can feel free to test that. In my opinion, the only plausible thing other than stat stages that might affect it is Sandstorm's Special Defense boost for Rock types, which I will check at some point soon.
Edit: Nope, 158 Defense, 157 Special Defense Tyranitar in Sandstorm keeps taking special damage from the 141/141 Slowbro.
Rising Voltage stuff:
Level 60 Jolteon 123 SpAtk Rising Voltage VS level 100 Togedemaru 153 SpDef
57 damage on Electric Terrain, then 27 damage after Togedemaru used Magnet Rise
This makes Rising Voltage 140 power on Electric Terrain if the target is grounded, which is then further boosted by Electric Terrain assuming the user is also grounded. If the target is airborne or there's no Electric Terrain it's just 70 power.