For marth's upB, basically, this is what would happen:
- No more invincibility frames 1-4
- the strong hitbox is bigger and moved slightly behind him, giving him a reverse upB to edgeguard with again
- the rest of the hitboxes are also made slightly bigger and are given more base, along with possibly sharper angles
Basically, it completely repurposes his upB. It's no longer a move he can spam to get out of a tough situation (you would in fact be better off spamming counter, which comes out one frame earlier), and it makes some "last minute" recoveries harder. However, it now comes with a few new advantages.
First off, there's the obvious edgeguarding implications of the initial hitbox. What may not be as obvious are the edgeguarding implications of the later hitboxes. I'm not sure about you guys, but I know that on numerous occasions I've recovered as my opponent was trying to come back to the stage (usually after I had hit them with a fair or some such offstage), resulting in them getting hit by the reverse hitbox on the tip of the sword as I grabbed the ledge. This would be great for edgeguarding if it weren't for the fact that the tip has so little kb. So while it's certainly possible to plan to hit them as you recover as it is now, it doesn't usually do all that much for you, especially if you need to be too far above the ledge in order to connect with it. With more base and possibly a lower angle, this would set up for bair edgeguards, though.
Then there's the matter of making marth's upB safe on hit, which is a fairly big one. While his recovery may be bad, if you hit them with your upB, you'll be safe, due to the raised base of the later hits. Unlike now, where you can still get edgeguarded even if you hit someone. So yeah, you need a few more frames to successfully recover, but if you get those frames, you're actually even more likely to make it back than you were previously, since if your opponent botches their edgeguard, they'll get hit, without the ability to punish you for hitting them.
I've yet to code any of this, but hopefully I'll get it done soon for you all to try out.
Now that that's over with...
Viet: The secret is in the growth. You can't lower the base much more than what I did without running into CGs (falcon can in fact just jump out on my setting, although that could just end up with him getting combo'd worse if the marth reads him, so...). Really, you just need to lower the growth a little more and it should be good.