How EXACTLY does the two-player mode work in Cuphead?

Disclaimer: I've been searching over and over for a detailed explanation of how does the two-player mode work in Cuphead, but there are tons of results linking to completely worthless articles from garbage sites.
So far, I've found exactly zero useful information, so I'm asking here.
So, is there an official or informed source regarding the 2-player mechanics?
Specifically:
- when there are two players, do the monsters gain more lives, more attacks, or what?
- if someone dies and fails to be revived, what exactly determines when he can come back? I've noticed that sometimes it's almost immediate, sometimes it's very delayed. Sometimes pressing start makes you come back, often it has no effect. No clue.
- is there any non-obvious effect? (i.e. not like "both have coins to spend", ok thank you very much, I can see that…)
While technically these look like multiple questions, THEY ARE NOT. The question is: is there a list of the actual mechanic differences in the 2-player mode? Those above are just examples of what such a list should include.
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Quick Answer about "How EXACTLY does the two-player mode work in Cuphead?"
- Boss HP is doubled when in 2 player mode, monsters are unaffected.
- If another player dies and is not revived by performing a parry on their pink heart, they are out of the round and will not return until wipe or stage completion.
How does 2 player work in Cuphead?
To get started in Cuphead co-op, simply connect two controllers, load up the game, and press any button on the second controller to have Mugman appear. You can also play with a keyboard and one controller if you wish, though sometimes you have to disconnect the controller in the menu for it to register.Does 2 player make Cuphead harder?
Two-player difficulty You'd think that having a friend to help would make things easier, but it doesn't. Yes, you can do more damage-per-second with two characters, but the game gives bosses extra health to adjust for that. So the increased attack power isn't an advantage.Does Cuphead have 2 player?
Now that Cuphead is finally out on Xbox One and PC, players are eager to load up the game with their friend for some local co-op fun as Cuphead and Mugman. Luckily, Cuphead's drop-in, two-player local cooperative mode is the easiest feature of the game so far.How do you play Cuphead 2 player without a controller?
If one keyboard and one controller are present, Cuphead will only allow them to be different players if the keyboard is player 1. To do this, press a key on the keyboard on the start screen. Once the player on keyboard has started the game, the controller player can join in by pressing any button.Cuphead- How to Play 2 Player (Details in Description)
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Marcus Aurelius, Zulian Yuliansyah, Marcus Aurelius, Marcus Aurelius