1. Append skill 5.

2. Yes, I guess.

Append 5 for sure, and yes, the crit up effect will stack for that turn only.

Ok I unlocked append 5 and it’s really good. I know I’m using event damage boost CE but he has 1mil+ HP so it’s fair. I also forgot extra attack also count as normal attacking so in total at the end of turn 3, she has 16 critical damage up. But I only get to use 14 so 210%.

For some reason I couldn’t believe it would stack but it doesn’t say it can’t like Oberon’s NP damage up which says it’s unshakable.

Well, crit up doesn't make nearly as much of a difference when you're using an event damage CE (especially an MLB one, it would make more of a difference if not MLB), but 210% up is enough to make a noticeable difference.

Ok I tried it without a mlb event CE. I’m using a CE that boosts Buster critical damage by 35% at a daily QP quest.

Here’s Melt at max crit up 260% on 3rd pic

I think you misunderstood my meaning. You're going to do way more damage with the event damage CE, it's just the diminishing returns are quicker to kick in because you're already effectively at +200% crit damage to start with so crit up will be far less useful than attack up or card type up, but like I said before, 200+% is big enough to make a noticeable difference. NP damage up is even less useful than crit up with the damage CE because NP buffs have smaller numbers.