http://classic.battle.net/diablo2exp/ba ... ence.shtmlhttp://diablo2.diablowiki.net/ExperienceSince monsters life was 200% (3 spawn), I figured you would get the same exp 1 spawn or 3 spawn (200%), I haven't found this so. I've always been able to notice an exp difference from having 2 mules in game vs riding solo.
As for monster difficulty, I assume you're talking about soloing or 3 spawning bosses and how they react? Boss AI is a mystery to me. Sometimes I think bosses will go nuts and move 2x faster vs a character with low vita, or using a certain item. We've all see Diablo target only 1 character in the party.....why...not sure. I don't think the player spawn has anything to do with it, I'm thinking more stats/skills/gear affects the boss AI making him seem harder.