Hiusi Guy said: (Source: #2241,
https://www.smogon.com/forums/threads/metagame-workshop.3709907/post-10973289)
When asked about Haze and Explosion, that would suggest surf would be single target.
Also your response just reminded me Choice Scarf Iron Head Jirachi is at least a consideration here.
Other concerns include:
Belly Drum + Extreme Speed, Sure it only starts on turn 2 and Extreme Speed is single target, but what are you supposed to do against +6 Extreme Speed? Especially if an ally has Ally Switch.
Spread Entrainment doing some REALLY dumb things especially since if I see this correctly, Arena Trap is legal.
If Counter/Mirror Coat becomes a spread move, it can lead to cheesy Focus Sash sets, especially if the partner has Fake Out.
Solar Beam or Solar Blade can be a spread move spammed from turn 1 with the only cost being a pokemon with Drought or a faster Sunny Day user being led. Weather Ball has a slightly higher level of power in sun or rain.
Rising Voltage is somewhat similar, but the question is Pincurchin or manually set? Also, ground types exist meaning it's not as bad.
Priority Spread Brave Bird. Actually, Priority Spread Acrobatics too.
Spread Trick sounds really dumb. IDK what it would do, but I know it would do something.
Spread Population Bomb is either terrifying or useless. I'm not sure which one.
Spread Leech Seed sounds annoying, though IDK if that would mean the same pokemon gets healed twice at the end of the turn.
Lastly, How would Strength Sap go if the user is on the right? Sounds like a massive heal for two pokemon.