Characters: Marth (me) vs Captain Falcon
Stage: Smashville
First match
No items, no hazards
The target test showed up for half a second then the game started as normal.
Right before the desync, he did an aerial falcon punch that landed on the ground and I dash grabbed him and tried to bthrow.

Characters: Kirby (me) vs Luigi
Stage: Dreamland
Items/Hazards: off
Multiple matches?: no
Anything else you should know?: After i got the luigi to 30% on the 1st stock he began to SD. On the last stock he taunted and then the match ended

Characters: Kirby (Me) vs ZSS
Stage: Dreamland
Items/Hazards: off
Multiple matches: no
Anything else: the ZSS started to SD randomly and right before the desync the ZSS taunted on her last stock

Characters: Isaac (both)
Stage: Smashville

Theres a problem im experiencing, im a hotspot user so 70% of the people i play with i experience Freezing at least once, there's other people whom i cant play at all (Oreocackester an example), the hotspot speed tends to fluctuate between 35 and 40mb/s download and 25-30 mb/s upload, ping very low, so i dont believe it is lag.
Characters: Any
Stages: Any, 3DS tends to fix it though
Hazards off, Item frequency Very High but all Items Off
Things that tend to fix it with some people:
Going 3DS
Setting High Latency
Trying multiple times

Characters: Kirby (me) vs G&W
Stage: Dreamland
Multiple matches?: No
Items and Hazards: off
Anything else notable?: he decided to continuously SD on his 3rd stock and right at the last time he SDed the match desynched.

Characters: Meta Knight (Me), Link (NO) and Jigglypuff (Rated R)
Stage: Peach's castle.
Items: On
Note: Rated R started self destructing a little while into the match. I followed and SD'd once myself.

Captain Falcon and Zelda
Battlefield
4 stocks all items off, hazards on (n/a)
1st lobby 1st game

Characters: Sora (Me), Link (xter)
Stage: Tower of Salvation
Matches: Single
Items/Hazards: Off
Note: We only played proper for about 5 seconds before he started firing arrows randomly. After taking care of his first stock there was a brief moment of proper gameplay, before going back to the way it was. After taking care of his second stock and accidentally doing a Side-B off stage, the game ended as soon as I got off the revival platform

What characters were used Sheik (me, P1) and Samus (P2)
What stage was used Tower of Salvation
If you played multiple matches in one lobby or if someone quit your lobby and someone else joined or anything weird like that This was the third game in the lobby with the same two players. Weird thing: Right when the desync happened, I got a notification that my opponent joined the match.
If items were on or hazards were on No

Characters:
P1; Wario (Snow Costume)
P2; Marth (Default)
P3; Kirby (Default
Stage: Waiting Room
Matches: First room, first match, right from boot-up
Items/Hazards: Both Off
Basic jist of what happened;
Match starts, was a 3-minute FFA
Connection was mostly smooth, a few jitters here and there but no notable signs of desync
Game ends, and then starts freaking the hell out
Screen switching from black to Victory Screen to starting the match again (I could tell because the Kirby Warp Star SFX plays on Frame 1 and I kept hearing that) with the text notifier spazzing and spamming the Desync Message, the "Room successfully unlocked" and "<User> has joined the room>" all at the same time rapidly

And then the game crashed.

Captain Falcon vs Link
Battlefield
4 stocks no time limit, no hazards no items
1st lobby 1st match

Characters: Megaman (Me), Mr Game and Watch (Opponent)
Stage: Smashville

What Characters Were Used: Captain Falcon Ditto
What Stage Was Used: Smashville
If you played multiple matches in one lobby or if someone quit your lobby and someone else joined or anything weird like that: 3rd match in the lobby
If items were on or hazards were on: Both Off
Anything else notable you think we should know: We were doing 40 stocks and this has happened to us at least 3-4 times

What characters were used: P1 , P2 , P3 (me)
What stage was used: Green Hill Zone
If you played multiple matches in one lobby or if someone quit your lobby and someone else joined or anything weird like that: We have been attempting multiple matches with the same 3 people.
If items were on or hazards were on: Items were completely off, hazards were off.
Also only P2 was desynced. P1 and my screen looked exactly the same.