Overview
While you usually won't be able to react and space perfectly, the general components of the video are all humanly possible to do. I'd say this kind of shield pressure is about as hard as the corresponding spacie stuff, but it varies depending on the technique in question. All the shield pressure variants are imperfect in that they don't keep the enemy shieldstunned permanently and can be rolled out of. Still the disjointedness and/or speed easily beat most out of shield options if used properly. The best ways I found to get out of Lucas' shield pressure are Shield DI to mess up the spacing and rolling, both of which can be dealt with if read. I didn't notice any effect of stale during my tests, but it may have an impact at high levels of stale. Note that I don't insist all of this will be useful in practice, I've just been gathering ideas.
Details
Ness: Standard pressure (
0:04-0:08)
(DownB->DJC FAir)*3
Generic shield pressure. Ness doesn't react and gets shieldbroken 107 frames after Lucas' first DownB connects. The next hitbox is active 7 frames after the end of the first FAir's shieldstun, 3 after DownB's. I sourspotted FAir during this sequence. Sweetspotting it would increase the shield stun after it by 1 frame, but it's hard to get the FAir sweetspot and still be in range for PSI Magnet.
Bowser 1 (Mars): FAir only (
0:10-0:11)
(DJC FAir)*3->Grab
This method relies on spacing alone. Bowser's UpB is too big for standard pressure to be safe, so DownB gets left out in favor of better FAir-spacing. Bowser tries to UpB in the 11 frames retaliation window after the second FAir, but gets beaten by the third one.
Sheik: NAir crossup & roll call (
0:12-0:13)
DJC FAir->NAir crossup->Turnaround DownB->Wavedash->Grab
NAir can be used to cross up opponents and mess up with their OOS-timing, but it has both more end lag than FAir. If timed as soon as possible NAir hits on the first frame opponents can jump/roll out of shield, but it gives the opponent opportunity to act for a few frames before the landing hit connects. If NAir is delayed by 4 frames like I did in the video the landing hitbox connects on the first frame after shieldstun.
Sheik tries to roll out after the crossup, but a wavedash grab easily catches it after being called correctly.
Ivysaur: Multimagnet v1 (
0:14-0:19)
DownB->(JC->DownB)*8->Fulljump OffenseUp
Ivysaur tries to Shield-DI away but ends off getting shieldbroken and subsequently killed via OffenseUp-wind. There's a 5 frame retaliation window between the shines, which makes this kind of pressure still unsafe against characters with fast out of shield options. Ivy's OOS options are too slow for that so her best bet would have been rolling, which takes 32 frames - theoretically enough for a human to punish on reaction.
This version of Multimagnet is relatively easy to execute, but isn't quite as good as the next one.
Jigglypuff 1 (Sleeping Cap): Multimagnet v2 (
0:20-0:21)
DownB->(JC-1>DownB->DJ->DownB)*2->JC-1>DownB
"-1>" means delayed by 1 frame
This is probably the nearest Lucas can get to perfect shield pressure. There are only 2 frames between shieldstun and an active hitbox after the ground jumps and apart from that the opponent is permanently shield stunned. Means that very few characters can do anything but roll/spotdodge and even with a godly UpB like Bowser you have to be nearly frame perfect to escape.
It's also the most difficult to perform shield pressure technique in this video.
Peach: Mixups (
0:22-0:24)
DJC FAir->DownB->DJC DAir->DownB->Instant NAir (Shieldpoke)->Grab
Peach's best chance of getting out of a standard shieldpressure combo would have been after the second FAir. A DJC DAir in its place hits 6 frames later messing up Peach's UpB timing and makes her shield eat DownB, after which an early NAir is guaranteed to connect with either Peach or her shield. In this case she gets shieldpoked and grabbed.
Fox: Shield DI to get out (
0:25-0:27)
(DJC FAir)*3->Wavedash->FAir
Fox Shield DIs, forces FAir only pressure and then comfortly gets out of it by shield DIing out of DownB and later even FAir range. Lucas uses his longer Wavedash and disjointed FAir to catch up with Fox and beat NAir, but can't reliably combo out of it because Fox falls too fast.
Snake: Working around the grenade (
0:28-0:31)
NAir crossup->Turnaround DownB->Double DJC-FAir->Combo
The NAir crossup has to be perfectly spaced and timed late enough to not eat the grenade but prevents it from getting in the way of subsequent attacks.
Squirtle/Marth: Baiting Up-B OOS (
0:31-0:33)
DJC FAir->DownB->DJC FAir->Punish
Squirtle's and Marth's UpB be both are fast enough to be used between FAir and DownB and have better disjoint than FAir. By spacing FAir wide enough away from shield Lucas denies himself a DownB-followup but also leaves Squirtle and Marth wide open for a punish, if they go for an upB.
I went for flashy punishes in the video, both are far from optimal.
Falco: DownB grab (
0:34-0:35)
(DJC FAir->DownB)*2->JC Grab
Of course, grab out of DownB can also be a viable mixup. It is easily spotdodged, though, if the opponent sees it coming and leaves Lucas wide open if it whiffs.
Falcon: Random semi-flashy stuff (
0:36-0:38)
DJC FAir->DownB->NAir->DownB->DownB->DJC DAir
Another PSI magnet instead of the DAir would have broken the shield as well and considerably faster, but I like the looks of DJC DAirs. : p
Mr. Game And Watch: Jab pressure (
0:39-0:40)
DJC FAir->(Jab 1->CC)*2->Jab 1->Jab 2
Mostly to show how fast you can chain Jab 1 into itself - frame wise this pressure is garbage. See "Frame info" below for a jab pressure retaliation window list.
Bowser 2 (Maritime): Multimagnet Mixup (
0:40-0.42)
(Jump-1>DownB->DJ->DownB)*2->JC->NAir->DownB
Bowser is one of the few characters who have an OOS option fast enough to escape Multimagnet pressure in his UpB. Still, the timing for it is very strict and a NAir mixup catches it (and any other OOS option) by hitting on frame 1 after shieldstun. In this sequence the only hole is the one after the first Multimagnet loop. The NAir hits on the very first frame after shieldstun and also would have shieldpoked Bowser's then tiny shield had he not tried to UpB (you can't see it, but he did).
The biggest problems with this pressure seem to be initiation and technical execution.
Jigglypuff 2 (Mars): Maximum distance spacing (
0:42-0:45)
DJC FAir->DownB (shieldpoke)->DAir
The running DJC Fair was used on the first frame for Lucas to still be in range for DownB after it connected. This distance is of course dependent on the opposing character and shield DI. A maximum distance DownB suprisingly shieldpokes Jigglypuff, setting up for just about any followup. Lucas chooses to try to go for a techchase after DAir, but unfortunately Jigglypuff can jump before hitting the ground and rests Lucas. Maximum distance SDI and worst possible DI secure the kill.
Toon Link: More Multimagnet (
0:45-0:47)
Bombcatch->Bombdrop->(DownB->DJ->DownB->JC)*2->DownB->DJ->NeutralB
The bomb actually doesn't do much here, but it hits one frame before the last Magnet and shows how fast this stuff is compared it. The more interesting stuff here is that you can initiate a (DownB->DJ->DownB->JC) just before landing from a shorthop and the usage of B-Reversals to cross up Toon Link.
Zelda: Magnet hold shenanigans (
0:47-0:49)
DownB(21)->DJ->DownB(10)->JC->DownB(10)->DJ->DownB(10)->JC WD->USmash
The number behind each DownB indicates how many frames it was held including startup.
Now we're getting tricky. First a floating PSI Magnet is used to initiate and held for one additional repitition (11 frames). The repitition hitboxes of DownB only have 5 frames of shieldstun/hitlag, so it offers a 6 frame retaliation window, which is 1 frame more than even Multimagnet v1. What it does, though, is let Lucas float to the ground with ok shield pressure.
The first 7 frames of holding actually don't increase the time Magnet is out due to startup, so each of the DownBs is actually only held for 3 more frames than necessary. When tapped the release hitbox would hit the opponent exactly 3 frames before he is able to act. The soonest frame any OOS option is invincible is frame 2 (spotdodges). Thus the effect of these 3 frames of additional hold time is that opponents who try to act out of shield as soon as possible get hit. This makes buffering rolls/spotdodges via C-stick unsafe when the input occurs too soon. Mind that using C-stick buffer still increases the window to input the command by 9 frames, but it can't be used at any but 1 frame of the whole sequence. You could also use different release timings to further mess with your opponents timings.
To get back to the video example. After floating to the ground Lucas starts usual Multimagnet pressure but with the release hitboxes delayed by 3 frames. Zelda tries to buffer a spotdodge but does it too soon and gets hit.
Frame info
All unstaled.
Advantage on shield:
PSI Magnet: +7 (Jump)
Sweetspot DJC FAir: -1
Sourspot DJC FAir: -2
DJC DAir: -3
NAir landing hit: -4
DJC UAir: -4
Jab 1: -8 (Crouch)
Jab 2: -17
Frame of the first hitbox:
NAir: 4
FAir: 5
UAir: 5
PSI Magnet: 5
PSI Magnet (aerial->ground transition): 8
DAir: 10
Lucas jump is 4 frames and DJCing an aerial takes at least one frame. Thus a perfect DJC FAir from the ground takes 10 frames until the hitbox comes out. For DAir the DJC has to be delayed by one frame or it hits the ground before the hitbox comes out. Same for UAir if you want the main hitboxes.
The second version of Magnet occurs when Lucas transitions from air to ground with DownB during v1 Multimagnets.
Jab pressure retaliation windows:
Sourspot FAir->Jab 1: 6 frames
Jab 1->Jab 2.1: 5 frames
Jab 2.1->Jab 2.5: 3 frames
Jab 1->Jab 1: 13 frames
Jab 2.5->Jab 1: 22 frames
Jab 1->DTilt: 11 frames
Each one in frames after end of shieldstun that the next hitbox comes out.
Move Timings in frames
DJC FAir/UAir (minimum airtime):
1: Shorthop
5: DJ
6: FAir/UAir
DJC DAir (minimum airtime):
1: Shorthop
6: DJ
7: DAir
JCed DownB:
1: DownB
10: Jump
Multimagnet v1 repititions:
1: DownB
10: Jump
14/1: DownB
Multimagnet v2 repitions:
1: Jump
6: DownB
15: DJ
16: DownB
25/1: Jump