Boss Centering

Hello everyone! I'm currently working on a Zelda-like adventure game and I'm setting up the first boss. I was wondering if it would be possible to reprogram one of the Monster behavior patterns to make the boss center themselves in the room and face downward? The battle's fun so far, but a lot of aimless movement with occasional chasing is a bit boring. I was hoping to send him back to the center to launch projectiles from time to time. Any help at all would be appreciated; I've been able to get as far as I have by copy/pasting chunks of .asm's into other .asm's, but in reality I have absolutely no idea what I'm doing.

what i'd do would be:
1) make the boss
2) when you defeat the boss, make a screen trigger
3) make a similar monster with the same animations and graphics, but in the center of the screen.
also, how do you even make a boss?

I'm guessing you could look at code that makes things move toward the player, but instead of moving toward the player, it moves towards a specific tile