My game Nitebear on Sleepystreet has a huge, alien frog boss that spits fireballs at ya on level 8. Also, at the end of most stages is a mini boss as an homage to Knightmare:
https://forums.atariage.com/topic/169496-nitebear-on-sleepystreet/
Thought it was pretty neat to use the playfield for the frog boss like what they did in Blaster Master on Nintendo. Was not as proud of the mini bosses since paradoxically making their shots move faster and wider made them easier to dodge somehow.