A Train Boss or Pacman could be good fun and a change from the usual boss in one place mode. The current limitation I can think of for the Pac man is some form of a location-based trigger, or on-collision-change-angle-by-90-degrees thing. I haven't quite figured out how to have an entity dodge 90 degrees to one side on trigger, but with a bullet-pattern moving the entity, it would be possible to do a simplified Pacman move system.
I've been working on code like this for a while now. I have an entity that will move in a direction on hit, but it doesn't know WHICH direction to go. However, if it is a fixed boss room, we could do some crazy things. Have each and the corner turns filled with 2 invisible entities. When the enemy boss goes into a corner, it hits one, based on which direction it came from. That entity then has the boss turn in the appropriate direction. Since the boss is already acting on a movement pattern, the second one won't change its behavior. T intersections would simply have some systems with a chance of happening and the others would always happen (unless the first does and put it into movement mode again). It would take a large amount of scripting to work.
If only there's an easy way to make a Free-Space style sweeping beam...?
I've been obsessing about this one too. My best idea so far is particles on a very high salvo or just a gravity laser with a low firing_rate. But then it is effectively always on and still have targeting issues, I can't get it to target where I want. On the other hand you can do fixed point targeting, which only will really work for a stationary boss. Although, thinking about it now, perhaps something like the the rotating shots Zharmad made recently might work out. There would be a lot of angle finagling involved.
That's what I was implying. Cardinal makes 90 degree turns when it runs into something. You can design a room to work with the and get the desired effect.
I spent some time on this with my first attempt at a pacman level. When a Cardinal mover hits a wall it chooses a random 90,180, or 270 path to follow. It will also ignore T-intersections and treat them as straightaways (for the most part). They aren't very good at doing anything rather than an aimless wander in a pacman style grid. The Zamboni did better a little better, but what was needed were all the variations of Zamboni movement, not just the right & down version. Mixing the movement types in the entities in the pacman grid was okay, but it really needed the pac pellets do make it really cool. I had tried a version with the maze filled with $1 credit pickups. That was actually really cool, and the sound effect was awesome. But they didn't want that much money seeded into a single miniboss room. Now though I have found you can have nondamaging shots that do the same thing, but I haven't pursued it again.