Let me talk about airdodging mechanics since I actually tested these a lot. Airdoding has a substantial landing lag but not quite as big as some make it sound; I'd say it's about as laggy to get the airdodge landing lag as to land during an average quality nair. However, there are no autocancel windows on either side of the animation, and I believe the extra lag even extends to landing during the animation's IASA. In other words, you have to be absolutely 100% done with the animation to avoid the lag when landing, and if you start up the animation and land, you get the lag even if you land before a single invincible frame occurs. Of course, that last point means that you need a little more precision than in Brawl to shield right as you land, and punishing landings is going to be a lot easier in general. In the match I played as Mega Man, I abused this by putting fsmash on top of people as they were landing. If they didn't airdodge, it would hit them out of the low air. If they did, it would tag them as they got the airdodge landing lag. There was just no way not to get hit out of that situation for them, and while this kind of set-up works in every smash game, I feel like it's especially strong in smash 4. I didn't get to test how airdodges canceled into tether attacks work which could be very important for those characters, but I think that's a pretty good handle on its general function.
One of the main reasons Brawl was so defensive was that run-away was so good, and it was no mystery why. 39f zero landing lag airdodges were crazy strong, and characters better at utilizing that to flee were ridiculously hard to catch. Combine with the forresses that were ledges, and it becomes clear how you can just run away with a life lead and slowly chip away at someone who dares approach. This change puts substantial and real risk to just running; your opponent can just put traps in your way, and you have a way worse tool to just keep evading. The risk-reward on doing that starts to look really poor if you aren't getting good attacking options regularly, and since ledges are now a disadvantage to go onto instead of an advantage, you can't just kill the momentum of risky positions by going to them. This kind of thing is why I'm so optimistic about smash 4; I already loved Brawl, but I didn't love everything about Brawl, and the things that were least lovable seem to be really carefully designed around this time. The airdodge mechanics are really one of the best demonstrations of that, and I thought they played great.
