While in hitlag you can wiggle the analog stick to move your character a short distance. The easiest and most prominent use of this is to escape from multihits, simply tilt your stick in the general direction you want to go then keep it fully extended in that direction but wiggle it around slightly (such as moving it from 20-40 degrees over and over again). You can SDI in any direction, although up and to the side will usually escape things the fastest. You can even SDI in if you want to extend their multihit forever and be goofy.

You can read more about how it works in Super Smash Brothers (it's very similar) here: https://www.ssbwiki.com/Smash_directional_influence

While shielding, you're restricted on what actions you can do, allowing a smart opponent to apply pressure to your shield and make it difficult to safely escape from it. These are all of the options you have while shielding.

• Up smash (Character dependent). Called charge attacks in this game, they're typically slower, and up ones typically hit above you. This is very character dependent, but many have good out of shield up smashes.
  
  
• Up special (Character dependent). Up specials tend to be slow and put you into freefall, but some up specials are good at escaping shield pressure.
  
  
• Grab (Usually around 7 frames). Grabs are pretty quick, but only hit in front of you and are easily punished if you consistently do them in response to shield pressure. Plankton is notable for having a frame 28+ grab, so if you hit someone out of shield with that they're probably asleep.
  
  
• Jump (Frame 3). Jumping is a fast universal option that frequently leads into good moves to counteract shield pressure. Buffering a neutral air is a great option on many characters, such as Spongebob who has a frame 3 nair (frame 6 from OOS due to 3 frames of jumpsquat). What aerials are good out of shield depend on your character.
  
  
• Shield drop (Frame 6). Dropping your shield takes 6 frames, during which you're vulnerable, and after which you're able to do anything you want. A tenth of a second might not sound like a lot, but if someone is applying proper shield pressure they can make many moves difficult to use with an extra 6 frames added on to the start of them. A good option to keep in mind, but keep in mind the extra startup as well.
  
  
• Spot dodge (Frame 1). Spot dodging will make you immediately intangible, but is easily countered if they're expecting it or using moves that are quick enough to punish.
  
  
• Roll (Frame 3). Rolls are like spot dodges, except they're briefly vulnerable at the start and move you.

If you receive sufficient knockback, the next time you touch the floor you'll enter a knocked down state where your only options are roll back, roll forwards, neutral getup, or getup attack. Your opponent can try to read your option to punish you, or reach you before you're able to use those options. Because of this, it's a great idea to not enter the knocked down state.

There are two main ways to not become grounded: teching, and a-cancelling. Teching is achieved by pressing the shield button right as you impact something. If you're still being knocked back you can tech off of walls and ceilings (allowing you to live theoretically forever if you always hit map geometry before a blast zone and never miss a tech), and if you're going to enter a knocked down state you can tech on the floor regardless of whether or not you're in knockback. If you tech on the ground you can choose to do a neutral tech, or tech while rolling in either direction by inputting shield and a direction on the analog stick.

The second way to avoid entering the knocked down state is doing anything before you touch the ground. Doing any action will take you out of the tumbling state and into a normal aerial state. You can throw out a random aerial regardless of distance to the opponent, use an up special for recovery, airdodge, anything will do it (although you have to be in an actionable state to do these, unlike teching). Using certain aerials while very close to the ground will interrupt them before they start, allowing you to land laglessly. This is called a-cancelling.

You can read more about how it works in Super Smash Brothers (it's very similar) here: https://www.ssbwiki.com/Tech

If you jump away from a wall while next to it, you can kick off the wall without using or requiring a double jump. I haven't tested it with every character, so some might not be able to do it.

Only one person can be on a ledge at a time, and anyone else who tries to grab the ledge will be unable to. Because of this, you can intentionally grab the ledge to prevent your opponent from doing so. If their recovery has no active hitboxes it's very easy, although if they can hit you during their recovery you'd need to time grabbing the ledge so that the brief period of intangibility you get from grabbing the ledge protects you from their attack.

This can kill certain characters exceptionally early, and can be very easy to do against many recoveries if they don't know how to counter it, but people might get upset if you do it since it feels a little cheap.

Most if not all special moves in this game can be b-reversed, including up specials and down specials. B-reversing a move will turn the move around, and convert your momentum with it. To b-reverse simply do a special move, then immediately flick the analog stick in the other direction. It's easiest to do with neutral specials.

A good way to practice and make it obvious when you're succeeding is to blow bubbles with Spongebob. Jump forward, then try to b-reverse a bubble. If you turn around and fly backwards with a lot of speed you b-reversed. If you do a side special you moved the analog stick too early. If you don't turn around you moved the analog stick too late.

You can read more about how it works in Super Smash Brothers (it's very similar) here: https://www.ssbwiki.com/B-reversing

If you airdodge into the ground you'll slide along it while in an actionable state. This game even has a shortcut for it, if you press jump and then instantly press shield you'll wavedash either forwards (neutral stick) or in the direction you're tilting the stick. Wavedashing allows you to have weird movement to be less predictable and quickly close gaps without sprinting so you can do normal grounded moves.

Despite the similar name, DI is not the same thing as SDI and is an entirely different mechanic.
Directional influence (DI) is a mechanic that allows someone receiving knockback to have a minor influence on how the knockback affects them. Tilting the stick left will adjust the knockback counter-clockwise, and tilting it right will adjust it clockwise. This can be used to make followup attacks harder, or try to dampen a killing blow into one that just barely wasn't lethal.

In order to use DI, all you have to do is tilt the analog stick in a direction while you're in hitstun before the knockback occurs. It's easiest to do with throws, since you have so much time in-between you no longer being actionable and the knockback occuring.

You'll always want to DI certain moves the same way, but that's learned on a per-matchup basis. Examples of utilizing DI are tilting the analog stick away from an opponent while being combo'd to try to escape from it with your increased knockback, randomly changing which way you tilt your analog stick when being thrown to try to mixup the way you get thrown, or these examples:

Aang's down throw sends you mostly up but a little forwards. Since he's using it while facing left, tilting the stick left (out/away from Aang) will cause you to survive longer, as it makes the knockback more horizontal and less vertical. If you tilt it right (in/towards Aang) it will make it more vertical, and kill you sooner.

Aang's forward smash sends you more forwards than up. Since he's using it while facing right, tilting the stick left (in/towards Aang) will cause you to survive longer, as it makes the knockback more vertical and less horizontal. If you tilt it right (out/away from Aang) it will make it more horizontal, and kill you sooner.

However, it does still have a considerable amount of vertical knockback, so if you're closer to the top blast zone than a side one (such as a high platform on the left side of the stage, while he's hitting you to the right) you would want to tilt it away from Aang to shift it more horizontal instead of vertical, and trying to DI it the same way as you do to protect from the side blast zone will instead kill you earlier.

Aang's up throw sends you almost entirely up but just a little backwards. Since he's using it while facing right, tilting the stick left (in/towards Aang) will cause you to survive longer, as it makes the knockback more horizontal and less vertical. If you tilt it right (out/away from Aang) it will make it more vertical, and kill you sooner.

However, Aang's up throw isn't actually a kill move at all, and is a combo move, so you should DI it the opposite way and try to maximize its knockback to make it difficult for him to followup instead of minimize its knockback to try to prevent it from killing you. You should DI away from Aang, to the right in this screenshot, to try to make as much distance between you two as possible.

You can read more about how it works in Super Smash Brothers (it's very similar) here: https://www.ssbwiki.com/Directional_influence

That's all I can think of right now for mechanics the game has that it doesn't tell you about. Let me know if you know of any others, or if you know if mashing (grabbed, shieldbroken), move staling, dodge staling, rage, or shield poking are in the game. I haven't noticed them if they are.