Name: The Hive
Power: <The Hive's Power is Equal to the Number of Players + 1>
Life: <The Hive's Health is Equal to the Number of Players x 10>
Ability: When The Hive fights, deal its damage to the first troop
in each lane and the Base. When a troop is killed, The Hive is restored Health equal to the killed troop's Health value and deal the Base damage equal to the killed troop's Power value.
This
boss is meant to be an optional post-Wave 3 fight in which The Hive sits (and remains) in the first zone of each enemy lane. 6 copies of The Hive card/token could be included in each game to visually represent this (this accounts for the 5-6 player addition as well). The encounter is supposed to create a race to beat the clock. The more troops that fall, the more difficult the fight is. Base damage is done slowly to show how massive the threat is and to give the encounter a sense of urgency.
The Power and Health were derived from having glanced over the enemy cards shown in Korsheth's post above and could be playtested/manipulated to work. The idea behind having variable Health/Power values is to allow scaling. The fight should not be trivialized by having fewer/more players, nor should it be any more difficult.
As for the theme, I was picturing a full on, Charybdis-style representation of the Xenosathem Hive bursting from the mining area to devour the Base. Here is a picture to help visualize my conceptualization of the beast.
http://www.fantastique-arts.com/photos/5746.jpg
Now, this theme can also be manipulated to fit the needs of the game designers. The boss might not represent a living embodiment of The Hive, but instead a large behemoth of a worm, sent from The Hive as a final champion, or just about anything large enough to fit the mechanics (and visual conceptualization) above.