Steven Ford said:

Hi,

Can you expand a bit more on the question please? Do you mean that your game currently assumes that all enemies are of a given type and you want to expand that or something else?

I tried asking the same exact thing yesterday, but the forum just would not let me post… :P
But yeah, having more detail as to what you're trying to accomplish, and what you're struggling with would help a lot.

Like the other people answering have said, I think that depends on the game, and on what you're trying to accomplish. If you don't want other enemies to be on screen while the boss is, I can think of three ways to do that:

1. The boss walks (or flies, or comes) into the screen when the player is at the end of the level and there aren't other enemies on screen.
2. The level is split by a door (or a portal, or a corridor…) that the player can go through, but the enemies can't. When the player has got through it, it closes so that the player can't “escape the boss” by going back (or you could allow the player to go back, but heal the boss if that would allow the player to heal indefinitely or something). The boss can't be attacked until the player is on the same side as the boss (and the door has closed).
3. Same as 2, but the boss isn't even visible until the player has gone through the door.

That's if you don't want the boss and other enemies to be on screen at the same time. If you do want the boss and other enemies to be on screen at the same time (and maybe even interact with each other), just don't stop the enemies from getting near the boss, or put the enemies next to the boss in the first place.

Also, you might want to make the level in a way that players can tell when they're about to get into a boss fight. That's another reason to use a door/portal/corridor.

And finally, you could think of what should happen after the boss fight, and maybe draw ideas from that. I hope that helps.