Is using the Ultimate N00b boss very repetitive in hacks (or not)?

I don't want to come across as ASM elitist and I certainly don't want to discourage learning new things, but if you can't get your hands on a good boss you shouldn't have a boss. If you can make one, fine. If you can get someone to make it for you (good luck with that), fine. But honestly, most (all?) bosses you can get from the site are pretty shite. If you make great levels and then stick poor custom bosses at the end of each world, it's just going to take away from the overall quality of the hack. It's better to not use bosses at all than it is to use bad ones.

I suppose this is as good a time as any to dump some of my boss design philosophy. At its core a boss fight should be a highlight of the player experience; otherwise there is no point to there being a boss in the first place. A boss should also be more of a challenge than the levels leading up to it, but not unreasonably hard. Usually this means that you should not introduce a lot of new mechanics during a boss fight as new elements are best introduced in a comfortable environment. As I said, bosses should stand out. To stand out, bosses need to be unique. I suppose that's a big problem with grabbing them from SMWC: They are used in a lot of hacks and a lot of them are fought the same way (by throwing things at them). It really makes most custom bosses from here more tedious than exciting, which is terrible for the overall experience.

Another thing making many bosses bad is that so many of them are designed the same way: dodge attacks, get projectile, throw projectile, repeat. It's terrible design that makes bosses come across as incredibly dumb for constantly using the one attack that makes them die (the DKC games are very guilty of this). Some other bosses you just jump on three times and you're done, which is just lame (this includes many official Mario bosses, but certainly not all).

So how does one actually make a good boss? The first thing you have to do is decide what kind of boss fight you want it to be. I like to generalize and put fights in one (or more) of four different groups based on the boss' aggressiveness: Overwhelming, aggressive, defensive, and retreating. Overwhelming bosses are ones you can't beat and you have to escape from; aggressive boss fights are the where you have to play defensive and wait for an opening (ideally not one the boss would deliberately give you); defensive bosses are ones where you have to be the aggressor and the boss mostly reacts to the player; retreating bosses are trying to escape. These groups are dynamic and many good bosses switch between them mid-fight. A great example of a boss that changes from one to another is King Zing from DKC2. On the level before the boss he is chasing you and you have to escape because you can't defeat him (which also serves as a killer introduction). When you enter the boss room he is passive and does nothing until you attack him, which makes him aggressive for a while; then he goes back to being passive again. After he gets low on life he goes aggressive until the fight is over. King Zing is a very dynamic boss and that really makes him stand out, especially in a game with pretty mediocre fights. The tempo dynamic of the fight is very important. An overwhelming boss can make the player feel helpless, while a defensive boss might make the player feel really powerful. Consider where in the game the boss is encountered.

The boss needs to fit thematically. You might want to think up some minimal lore, even if it's never presented to the player. It makes it easier to give the boss a design that doesn't feel out of place. Some dialogue is great for giving bosses some characterization if you want to. The background music is also incredibly useful for conveying a certain atmosphere. The tempo of the music should also fit the overall tempo of the fight. Is your boss really slow? Then don't use a fast and super-intense song.

The last thing I want to talk about is boss AI and combat mechanics. This is usually what takes the by far most time. The boss needs to behave realistically (relatively speaking) which above all means that the boss should react to the player. This is important for making the fight involving. The player will always react to the boss, so that's not really an issue, but the boss should be influenced by what the player is doing as well. This is more important the more defensive the boss is, but is still very much relevant for aggressive bosses. Does your boss shoot a projectile? Make it aim for the player. A very common mistake in combat mechanics is not letting the player hurt the boss unless it performs a specific attack. If the boss could theoretically make itself impervious by using only safe attacks your design is flawed. If the boss can't be hurt at any time it shouldn't expose itself to danger unless it's also the only way to hurt the player.

Wow... that was pretty long. I hope my message came across well enough.

That's what hard usually means though. Once you know ASM you can do anything with it; we say some things are harder than others because they require more research and effort and take longer to learn how to do. Making a good boss takes a lot more effort than many other ASM-base tasks so it makes sense to say it's harder. It might be easy for someone who is very experienced, but then it's still hard by comparison.