Custom bosses are my personal favorite as bosses are very fun to fight. This may be the most restrictive as certain types of bosses may not work in certain games, but you still have a lot of opportunity as there aren't any real limiters when it comes to what the boss can look like and it’s attacks and name can be. Usually beginners will go off of preexisting models and use them to make similar but different types of bosses, then once they are more skilled they go off and make completely unique designs and create custom, one-of-a-kind bosses. As stated with enemy types, make sure your boss works well with the type of area you'll be setting them in and if you end up adding in minions then have them go in tandem with your boss so it makes more sense, that way you can help insure things run smoother and make your boss all the more notable.
