This guide is an extended version of my previous guide for the 1st Impact demo.
There is a lot of stuff the tutorial doesn't cover properly, so here you are some generic tips and tricks to get started:

• if you can consistently outmash your opponent, go full speed ahead, because they won't stand a chance at winning the mashing minigame, unless they use Twain OR they outplay your mind games
  
• if you are consistently outmashed, buildings and mobility are your friends. Mashing doesn't help against a fast moving skyscraper thrown in your direction
  
• if you rush an opponent, you can end a clash with a throw instead of a punch. This can help if the opponent is better than you at mashing
  
• the first recovery prompt is almost unuseable do to it being very fast, so a follow-up attack after sending the opponent away is almost guaranteed (unless the opponent is using Groovis and his Avoid passive skill is active)
  
• doing nothing during a clash triggers the Taunt. Taunt wins only against Counter (or if the opponent gets a Miss by mistiming their button press during a clash), and gives the taunting player full meter and a free attack. As risky as it is, it is another level of mind games

Concerning the various characters, while the statistics are the same for every one of them, each one has a different passive skill (which triggers after a certain time or if you have been dealt enough damage) and active skill (the super move):

• Armoir has a super with gigantic hitbox and his passive skill makes you deliver a full power punch at the next clash, no matter when you press the Attack button. This punch will overwhelm any normal Attack (even on the same intensity), but will lose against Counter
  
  
• Shin's super is a 270° kick with short range but doesn't require aiming. His passive makes him faster than anything else, which makes it easy to throw buildings at full speed or catch a recovering opponent
  
  
• Skelly's super has a decent hitbox and her passive creates a lot of low-damaging bones which disrupt the opponent's approach. PLEASE, notice that Skelly's passive is different between the demo and the full game Since 08.06.2020, Skelly's passive is the same both in the First Impact demo and the full game
  
  
• Groovis's super has a very small hitbox and needs precise aiming, but it's almost instant. His passive makes him auto-tech when thrown away and improves his survivability to death QTE
  
  
• Twain's super has long range without moving away. Their passive allows them to win easily every mash contest while it's active. PLEASE, notice that in the demo this used to be Skelly's passive Since 08.06.2020, Skelly's passive is the same both in the First Impact demo and the full game, so Twain's skill is theirs alone.
  
  
• Jetto's super is a salvo of slow-ish missiles that fly in a straight line (albeit with a bit of tracking) with decent range. His passive skill is a sort of "instant transmission", allowing him to teleport instantly without having to wait for it to reload, making him a literal combo monster and allowing him to move around and reposition himself super fast
  
  
• Buya's super has him transforming into a giant ball and smashing in a straight line against the opponent. It's not the fastest super in the bunch, but has a humongous hitbox. His passive makes him able to break down his dashes suddenly and change direction at straight angles at max speed, making him extremely unpredictable. Buya's super can go through Lord Rekt's Black Hole, but doesn't save him from being caught if he hits Lord Rekt inside it
  
  
• Wiggle's super has her ramming against the opponent full speed, swallowing them, and throwing them in the opposite direction. Her passive lays bombs wherever she moves. Those bombs can be used for damage or combos, effectively making the stage play against the opponent. Wiggle's super can go through Lord Rekt's Black Hole, but doesn't save her from being caught if she hits Lord Rekt inside it
  
  
• Lord Rekt has a very dangerous super with a very huge active region which stands on screen for several seconds. His passive is pretty weak, as it just causes objects and super stars to be attracted by him. Lord Rekt's super can literally save you: when the opponent is sucked inside the black hole, you get teleported just above him, no matter where you were on screen. Lord Rekt's super must be aimed in the opposite direction with respect to the position where you want to place the black hole
  
  
• Bud is broken, as all arcade bosses should be. His passive completely stops the opponent's momentum and the momentum of everything thrown at him in a very large radius. His super is a 360°, humongous area super that hits instantly - which can be avoided once in its active zone only if you are using Jetto with his passive active

Mashing is a main component of this game. If you are outmashed, you will be at a striking disadvantage against your opponent. Currently, there are players reaching up to 15-16 clicks per second on either keyboard or mouse. One way to check your mashing speed is to use this (non-affiliated) website here:
https://www.shmupspeed.com/
To get your clicks-per-second, just divide the result by 10.

If your mashing speed is slower than 10 clicks per second, you might want to follow some tutorials on how to mash faster. One of such tutorials can be seen in this YouTube video.

If you are consistently outmashed, stage knowledge, throwing objects, careful teleports and positioning can help you get the upper hand, even though it is definitely an uphill battle.

You can change the number of rounds for arcade mode by changing the number of rounds in the options. You can also change the difficulty to Easy if the arcade boss is too hard at Normal.