Request for Champion aggro explanation, and QoL for Fiddle

Outside of taunts, I'm not sure how champ aggro gets turned on.

I know u turn off ur autos with S, which also makes u stand still. Sometimes the champ starts autoing minions by themselves, sometimes they don't. I'd like to know if it's the type of champ (auto based like marksman) or range or having taken dmg, what exactly turns it on and onto what - minion or enemy champ. Jhin for instance is so annoyingly trigger happy that sometimes I just can't walk around minions long enough to trigger the crit on an enemy, it goes off on some random minion. But I'm here for Fiddle.

After I W (drain) a jg monster, it won't auto that monster, or any other in that camp, unless I auto'd before the W. It's always been like this, not saying this is why Fid's winrate is where it is rn. It's just my gripe. Wouldn't it make sense to do basic attacks after an ability? In a lane, too, I have this huge wave and other champs will go on auto'ing them minions, but not Fiddle. Whether I used abilities or just AA's, doesn't matter. It will just sit there dumbfound. Same with Fid's aggro on champs, I'd like to have aggro on that champ after I used an ability on them. Maybe sometimes I lose it cus they go in a bush, idk if by default it's always there, hence this thread to better understand aggro.