I did more science and figured out all the attacks in the game that can make opponents trip.
If you hit the other guy with one of these moves when his percentage is in the range listed next to the move, there's about a, oh, I dunno... 10% chance he'll trip. Except for the moves marked with a *, which trip about 50% of the time. Very useful, to say the least. Those are the ones you need to watch out for.
Moves marked with a ? aren't that reliable, but I marked them as worth taking a look at because they can cause tripping over a large range of damages.
Basically * or ? = useful
So what happens?
Basically, tripping can occur with moves that send you opponent straight horizontally (kind of I guess), so that they slide across the ground stunned, or with moves that launch them by hitting them down into the ground (like using many dairs on grounded opponents). When you hit an opponent at low %s with one of these vertical launchers, they'll stay grounded.
But if you use the move when your opponent has enough damage, they'll get launched. Bowser needs 52% (in training mode) for Mario's fair to launch him.
For these moves to be able to trip, the opponent's % needs to be low enough so they're not launched, but higher than a (seemingly arbitrary) threshold. Bowser must be at 18% or higher (but lower than 52%) for Mario's fair to have a chance of tripping him.
Moves that send your opponent horizontally follow the same basic rules. Mario's ftilt, at low percentages, will send Bowser sliding stunned along the ground in his HUARGH animation.
HUARGH!
But once Bowser reaches a high enough percentage (46% in training mode), Mario's ftilt will put him in a WHARRGARBL state.
WHARRGARBL!
To cause tripping, they must not have so much damage that the move WHARRGARBLs them, but again, they must have enough damage that they're within tripping range. Mario's ftilt can only trip once Bowser has 38%, but stops being able to trip when it WHARRGARBLs him at 46%.
Jigglypuff is HUARGH
Usually a character's WHARRGARBL animation will involve one or both feet leaving the ground and them becoming unbalanced.
Another important distinction between HUARGH and WHARRGARBL is that
HUARGH'd opponents will bounce off walls (and be forced to tech), while WHARRGARBL'd enemies will just kind of WHARRGARBL in place against the wall. This might be useful, I dunno.
NOTE: These were all tested on BOWSER in training mode. If you want to find what percentage a different character will trip at, you have to DIVIDE these nuuuuuuumbeeeeeeeeers by another nuuuuuuuuumbeeeeeeeer depending on the weight of the character. Jigglypuff's number is 1.32. So to find out when Zelda's dtilt will stop tripping Jigglypuff, you divide the upper range I gave (92%) by 1.32, which gives you 69%! I've tested this and it works, though I don't have ratios for anyone other than Jigglypuff right now. But you could probably derive it with some numbers on character weights.
NOTE 2: Being that I did these tests in training mode, these nuuuuuuumbeeeeeeeers also don't account for Stale Moves. Spammed attacks diminish in knockback, so the percentage range for a spammed attack will be higher.
NOTE 3: Being that I did these tests in training mode, these nuuuuuuuumbeeeeeeers also don't account for the bizarre fact that knockback seems to be just slightly reduced in training mode. So though Mario's fair can trip until 51% in training mode, it only trips up to 48% in a regular match. It is teh mysterious ¯\(ºдಠ)/¯
NOTE 4: The slope your opponent is standing on affects HUARGHing and WHARRGARBLing (but doesn't affect attacks that launch). If you hit them downhill, they'll WHARRGARBL at lower percentages. It's the opposite for hitting them uphill. These nuuuuuuuuuuuuuuumbeeeeeeeeeeeers are all for opponents on level ground.
NOTE 5: I don't believe DI has any effect on this. Unlike melee, SDI and ASDI cannot change what hit state you are sent into, so you cannot SDI downwards to stay grounded, or SDI upwards to make yourself WHARRGARBL instead of HUARGH. And if a move would send you flying at a low angle, you can't DI downwards to keep yourself in a grounded hitstate (though you can make yourself bounce or tech off the floor). But I believe you can ASDI/DI sideways near a wall to tech into it (this would allow you to ledge tech, so someone should look into it.) But I think you have to press L after being hit, which gives you like 1 frame, lol.
NOTE 6: AIRBORNE TO GROUNDED HITSTUN: If you hit an airborne opponent into/onto the ground, they'll either bounce+need to tech, or WHARRGARBL (if their damage is low enough). The maximum amount of damage that will make an airborne opponent WHARRGARBL is the same as on the ground. Falcon's dair, for example, will WHARRGARBL an airborne (or grounded) Bowser at 37%, but at 38% it will make him bounce off the ground (if they're grounded, it will send him airborne). This means no tripping of airborne opponents (since they never HUARGH).
nuuuuuumbeeeeeeeeeeeeers
All numbers pretty much exact, unless preceded with a ~. You can be sure I got the upper boundaries right, but it's possible I made a mistake with the lower boundaries. I might have also missed some moves, so if you see something trip that's not listed here, tell me!
fs=forward smash, dt=down tilt, nair=neutral air, etc
Remember, all of these percentages are against BOWSER!
PIT
*ds (front) 0-8(13 dmg) 0-10(12 dmg) 0-27(10dmg tipper)
?us (first hit) 0-999
ft 19-24
fair ~21-29 (there are different damage versions but whatever)
bair wimpy 49-59
uair last hit 2-7
LUCAS
*dt (tip) 0-999
ft 15-24
bair(9 damage version) 10-18 wiener version 93-107
fair 19-23 wiener version 26-31
dair last hit 47-97
SNAKE
*ftilt 0-999
*dair 2nd+3rd hits 0-999
CAPTAIN FALCON
*fair wimpy 0-38
uair 17-23
bair 3-7 wiener version 19-26
?dair 13-37
ftilt 26-31 upwards variation: 22-27
ds back part 3-7
ZELDA
A 34-46
*dtilt 0-92
fair+bair (they're identical) wiener versions 113-128
?dair wiener version 80%-141
SHEIK
nair(strong part) 25-30
bair (11dmg ver) 31-39
needles 291-999
chain (electric) 45-62
FALCO
*dB 0-122
upB ~150
?dair 16-41
bair 25-30 wiener version ~9-13
ft 45-50
METAKNIGHT
*dt 0-82%(exact)
ft 71-85%(exact)
fs 0% (And ONLY 0%), 1% is full flinch
nair 0-1%
fB at low %s
MARIO
ds (back part only) 0-5
ft 38-45
nair 13-18
bair 18-26 wimpy version 55-64
?fair 18-51
fs 0-1 fs wiener version0-2
MARTH
middle A 133-158%
tipper A 29-42%
middle forward A 17-25%,
middle bair 1-9%
tipper bair 0-1%
middle fair 0-3%
middle dair 8-15%
tipper dair 0-17%
middle uncharged b 3-10%
IKE
fair 5-10
dair 0-3
TOON LINK
*dt 0-30% (exact)
ft wiener hit ~ 20, who cares, too hard to get
*Dash attack 0-999
*nair 0-18 (exact)(front and back)
fair ~0-7
B full charge ~75
?dair 0-12
SAMUS
A 137-156
fs (low ver) 8-12 (mid ver) 5-10 (high ver) 3-7
ft (mid ver) 41-48 (low and high ver) 26-31
ut 0-10
dair 18-40
bair wiener 1-7
nair 46-54 wiener version 70-81
B uncharged 248-284
homing missile 374 -999 (trips rare though)
bomb ~152-175
ZERO SUIT SAMUS
*ft (low ver) 0-33 (mid ver) 0-60 (high ver) 51-60
Thanks Tristan_Win
fs 0-5
dash attack 17-27
dair (first part) 8-21
fair (first hit) 15-28
PEACH
bair 0-5 wiener version 74-86
nair 9-14 wiener version 43-50
upair wiener (11 dmg) version 34-39
BOWSER
*dt 0-7
nair 14-20
LINK
A 225-260 jiggs-197
ft 7-11
fs (1st hit)0-4
nair 10-16 wiener version 38-47
fair (1st hit) 38-43 (2nd hit) 4-8
arrows (full charge) 76-86 no charge 201-226
DIDDY KONG
ft 22-27
ds (back part) 0-6
?dair 0-23
fair 0-5
bair 1-8
B peanuts some super high number
*fB (14 dmg ver) 0-7 (10 dmg ver) 0-18 (there's a rare 12 dmg version but I'm not getting it)
**banana
ROB
*dt 0-100
ft 8-17
?dair 0-27 wiener version somethingwhocares-56
fair 3-10 wiener version 14-24
fB (later hits) something very high-264
FOKKUSU
ft 40-47
fs 12-16
us wiener hit 16-20
dair 114-309 (annoying tripping can make you miss next hit D: )
nair 30-36 wiener version 67-76
bair wiener version ~30-35
WARUFO
*dt 0-27
*fs (wiener version of 1st hit) 0-239 (very hard to land, though)
bair (13 dmg ver) 7-11 (10 dmg) 16-20 (11dm)15,17
??dair 19-44
nair (last 3 dmg hit) 78-96
DEDEDE
*dt 0-18
bair 0-10
dB (uncharged) 10-15
fair 10-14
CAPTAIN PE
NISFACE
ALL THE PIKMIN DO DIFFERENT DAMAGES F
UCK YOU POOPIMAR
fair (purple) 2-6 (red) 0-5 (blue) 2-8 (yellow) 6-11 (white) 30-41 Damages, for comparison: p14 y12 b13 w5 r15
dair (p) 0-17 (r) 0-11 (b) 0-17 (y) 0-23, (w) 3-42 w8 y12
ft 20-25
fs (p) nevar (r) 13-16 (b) 12-16 (y) 18-22 (w) 46-54 (there's a wiener version but who cares)
GANNONDIRF
jab (9 dmg ver) 0-6
bair 0-1
?uair (6 dmg ver) 57-999 (8 dmg ver) 43-999
nair (2nd hit) (7 dmg ver) 14-22 (5 dmg ver)22-33
NESS
A 237-
*dtilt 0-999
ftilt 20-25
nair 10-15
bair 5-9
fair (last hit) 0-18
?dash attack (first hit) 0-999
fsmash (on 45º upwards slope) 0-5 (NOTE: when undiminished, this attack is too powerful to trip, and will always WHARRGARBL unless it's hitting uphill or stale)
PIKACHU
?A 0-999
dash 0-11
ftilt (mid ver) 23-29 (low ver) 25-34 (high ver) 19-25
*dtilt 0-45
nair 5-10 (wiener)28-37
dair 17-23
?B 106-155
*fB (uncharged) 0-4
?uB (first hit)310-999
DONKEY KONG
A: (first hit) 93-105
*dtilt: 0-61
ftilt: (mid ver) 27-31 *(low ver) 0-36 (high ver) 19-23
dair: 0-9
fair: 0-19
bair: 5-10 (wiener) 35-42
nair: 10-15 (wiener) 36-42
B: (uncharged) 19-25
uB: (last hit) 0-7
MR. GAY AND WATCH
fair: 0-1
hammer (#2) 0-something (#7) something-something yeah G&W sucks at tripping
JIGGLYPUFF
A: 236-267
ftilt: 28-34
dash: 12-17
fsmash: 7-10
?dsmash: 4-999
nair: 18-24 (wiener) 85-98
bair: 24-30
?dair: 65-162
fair: (wiener) 80-93
WEEGEE
*dtilt: 0-108
ftilt: 36-42
dash: (not last hit) something-291
fair: 8-15
dair: 10-15
bair: 17-21 (wiener) 32-39
Soon to come: Furries!
FAQ SECTION
Q: holy crap WTF OMG what is this I don't even 
A: ¯\(ºдಠ)/¯
EDIT: THIS TECHNIQUE AM NAMED 'DLX HUARGH-CANCEL'
Linear Mode
