Far Reaching Systems Changes:
1) No longer a strict d20 System. d20s are a part of the game, but not the exclusive resolution of all systems.
Especially when something is competitive between two characters (whether PC, NPC, or monster), this seems huge. There are some things random enough where my +1 bonus self might have a chance of beating a non-epsilon chance of doing better than a +10 bonus. So if it's two people who know the rules playing a single game of MtG, maybe it's competing d20's with modifiers - anyone can get screwed/flooded, but there's still a skill difference. But a typical just for fun chess player isn't going to beat or draw against the grandmaster, even if spotted a few pieces. And even the master is probably not going to be able to pull it off very often. Maybe that's d4s with modifiers added.