A simple suggestion, because getting the same boss five times in a row (especially if it isn't Hans or Patriarch) is really boring: Make it so that the boss wave cannot have the same boss the last boss wave had. If you got abomination (lucky you 
) last boss wave, this boss wave it must be Hans, Patriarch or KFP and cannot be Abomination again (thank goodness ).
A slightly more complex potential implementation of this would be in the form of a boss "pool." The pool starts out full, with every boss in the game in it. Every time a boss is randomly chosen for the boss wave, it is eliminated from the pool. When the last boss in the pool is killed, the pool refills with all bosses but the last boss fought still cannot be the next boss wave boss.
) last boss wave, this boss wave it must be Hans, Patriarch or KFP and cannot be Abomination again (thank goodness ).A slightly more complex potential implementation of this would be in the form of a boss "pool." The pool starts out full, with every boss in the game in it. Every time a boss is randomly chosen for the boss wave, it is eliminated from the pool. When the last boss in the pool is killed, the pool refills with all bosses but the last boss fought still cannot be the next boss wave boss.