when there is no annoying useless runner class
Debatable, but this ain't the Drama Forum even if I don't see the point in banning an annoying class, since it can be an advantage.
[] Boss Models
[] Infiltrator Class
Boss Models would definitely be good, but can be an issue at times if you fill up the datablock too much. Otherwise, that's a thing to consider.
Remove Medics in favor of Health pickups.
Don't make the boss too small and impossible to hit, it should be around 1.5 in player scale.
You aren't fighting Sonic, tone the speed down if players have trouble hitting the boss.
The boss should not be able to kill people in one hit.
Do not have a "store"
Auto kill players staying in the spawn
If you're going to have a slow moving class give it an extra movement option.
TEAM WORK SHOULD BE A WINNING STRATEGY
Lot of crap to cover, but will address in the order given:
Health pickups can be abusive without the right events, but a good notion than an expendable player.
Boss sizes can be overrated when it comes to guns and aiming, unless you fill loadouts with wooden planks.
Speed can act as both an advantage and a disadvantage, especially in a physics based game.
One-hit KOs can be unfair. It's just that...yeah forget it, it's definitely unfair.
Define your version of a 'store', because it can mean a lot of different store mechanics.
Auto spawn killers are a must for idle and nooby players alike.
Slow moving characters can just be a base for heavy weaponry. Nobody likes a fast player with a Mini-Nuke.
And sadly, there seems to be a very short supply of teamwork from where I stand in a Boss Battles server, since people 'done goof'.
For the love of god, think of the balance between classes
Always a large consideration.