Reverse Warlock Punch would only do 84%, you'd need something stronger to hit the cap of 88% (Like Bucketing 3 PK Flashes ), that being said since I doubt we're ever going to counter anything stronger than a reverse warlock punch in an actual match I think it's fine and we can assume it caps at 88%.
Yeah I did some labbing with this & came to the same result that
Hyper Buster's cap is 88%.
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About Back Slash Charge aka BSC (before I dismiss it & talk about sets perhaps)
-Distance | ★★★★★ (5/5)
-Range | ★★★★★ (5/5)
-Super Armor | ★★★☆☆ (3/5)
Distance
So the distance is for sure fantastic. To put this to perspective, imagine yourself trying to use Back Slash from a mid-far distance to go for a landing punish, with their back exposed to you. Now imagine the Back Slash barely missing them by a hair even though the tipper area of Back Slash is oh-so close. If you felt bad, don't worry about it, because Back Slash Charge would of put Shulk much closer to hit with the red Monado blade itself
(11%) compared to the Back Slash you almost hit with
(14% if you were airborne hitting with the Beam or 13% if you landed on the ground tippering). The distance is definitely a core reason we'd use this Custom, including the other qualities BSC possesses.
*A tip* = If you find yourself overshooting distance, then utilize reversing the BSC's direction in the middle of your leaping animation to reduce the distance you commit to. This helps you with controlling the position so that your landing slide will look shorter. And finally, you can also delay reversing your direction if desired.
(Example #1: You start pressing BSC to the left but you're a bit close that you might not hit them, so you reverse your direction by tapping to the right & then tap left again, aka WaveBouncing when doing it in a quicker manner)
(Example #2: You're facing right & want to BSC to the left, so you BSC to the right first & then tap to the left, aka B-Reversing when doing it in a quicker manner)
A Conclusion: Monado Arts do not affect BSC's distance it travels when charging forward or when BSC is falling down. But one thing that's interesting is the
Speed Arts reduce the distance you slide across the floor, which may or may not tickle your fancy. Their increased traction could make Shulk safer because he won't be over-extended but could ruin the sliding hit-box's range since you travel less distance.
Range
The range of BSC is mostly clouded by how far the distance is, which is understandable hence BSC emphasizes on the charge. However, BSC's range ties in with the distance, & it's range greater than BS or BSL because Shulk landing on the ground & sliding across the floor / terrain is also a hit-box too
(not all of the Monado is a hit-box while sliding though). For a reference, this sliding hit-box can hit someone after they roll or spot-dodge as well. And like I said above in Distance, a
Speed Art reduces the range of the sliding hit-box, which can be either good or bad depending on how high the traction increase decreases the slide length
(Hyper Speed really makes BSC come to a stop, meanwhile Speed doesn't reduce the slide by too much).
Super Armor
This is what I'm really feeling about BSC. I haven't gotten the full gist of BSC's Super Armor like per-say how many frames it lasts or if there's more Super Armor near the end of the falling, but the duration I'm seeing is not so bad
(it could be better or worse). Putting Shulk's SA frames in BSC to the test, I figured out that he gets Super Armor the moment you input the move
(I won't flat out say it starts at Frame 1, so I'll leave that to the datamining). To figure out when exactly the SA frame window ends, I had a Shulk collect the 3 Daybreak Parts & create the DayBreak & timed the laser hit accordingly to BSC's startup & see where it ends. I don't have pictures or video, but basically when the Monado swung overhead starts showing that
after-effect dragging a trail in this color. That's around the exact moment Shulk loses Super Armor
(or for an easier example, Shulk wielding the Monado directly above him facing right, the Monado is positioned sideways with a bit of that dragging trail to it).
Basically, I see the Super Armor getting utilized for those tight moments you need it for when you're coming to the stage & need to BSC against a charging smash attack after being ledge-trumped, or a terrifying move like Ganon's Warlock Punch or his U-tilt. BSC would charge through the festery & think nothing of it. This also favors trading moments you'd rather take damage than dying, so I say go for it.