What makes a boss good?
I think a good game to study the bosses is hollow knight, for my game I wanted to start with one of the more complex bosses. The idea is that this boss will be hidden behind doing some hyper specific quest or through glitches. The complex bosses in hollow knight tend to have about 5 main attacks, some bosses like pure vessel use more attacks when the hp is below a certain point or have an attack almost work as a marker of your progress (grimm and nkg use a pumpkin attack everytime the player removes 1/4th of their hp).
My inspirations:
For the duck specifically I wanted to have a bunch of laser based attacks (since everyone knows ducks shoot lasers). I had a random bullet hell related fixation at the time (and possibly still do) so thats why there is a bullet hell attack. Hollow knight is obviously a huge inspiration for me with enemy design, since its able to jam so much flavor into a fairly simple combat system.
Design principles:
1. Consistency: With any boss in almost any game you want them to be consistent and fair, this means all of the attacks should
have some way to dodge every time. An important thing to remember is that you as the developer will be better at
the game than the average player, because of this you want to be able to beat your boss without getting hit. This
also proves that the boss has a good level of consistency and is at least mostly fair.
2. Weakness: Bosses (and enemies) have 3 major stats, in most games these are speed, attack, and defense with anything you
fight (and are able to win against) you only want to focus on 2 of these 3 and have one stat be low. An example from
hollow knight might be hornet, hornet has a fairly complex moveset and she's fast this works because here health is
fairly low and she staggers pretty frequently. Another example from hollow knight is the paint master, they have a complex
moveset, don't stagger super frequently, have a high amount of health and they are slow to balance it.
3. Telegraphs: This has a lot to do with the fairness of a boss but nearly every well designed boss has a windup to their attack
this is called telegraphing and is one of the most important things you can do to make your bosses not suck.
If you don't have time to react to something you aren't going to react to it, if you think telegraphing makes bosses to easy
you can extend the length of a telegraph to bait out an early dodge and punish it with higher damage (this is done a lot in souls games).
I think the minimum amount of time you can telegraph an attack would be about a quarter of a second, if it is this fast it should
be balanced in some way (like maybe lower damage, a long wait time post attack, etc.).
In summary, a good boss is something a player can beat without relying on luck and is purely skill reliant.
The "Oh yeah I'm also making a game" part
Its gonna be a very movement focused metroidvania with bombs as the gimmick, it's very celeste speedrun inspired so you can clear most rooms in a few seconds if you have the bomb ability. I may or may not also include a ton of content that you access through doing glitches like wrong warping and stuff.