>>95992725
>Mechanics
The boss has either massive damage reduction or straight immunity to damage unless a condition is met or action is taken. For example, an Umbra suffers 90% reduced damage against energy, rending, impact, and explosive damage types, but other damage types inflict normal damage. In turn, the umbra has low health compared to an equivalent enemy, to reward those who prepared with alternative damage types.

Alternatively, a boss simply cannot be damaged due to esoteric or technological means, and the players must solve this during the fight before the boss is damageable. For example, the boss is covered by an impenetrable energy field from a blackstone projector inside them. However, player research has found this blackstone projector is positively charged. By standing next to a negatively charged blackstone projector in the environment, the players can daisy-chain an energy link from negative terminal to positive boss, blowing out the boss's shield and making it damageable. All the while, additional enemies and maybe even the boss are attacking the players. This lets the players have an active hand in weakening the boss, and preventing everyone from just buffing up and melting in an immobile alpha strike. A GM can get creative with mechanics, but it's wise to introduce your mechanics in a safe and experimental way beforehand, for example, letting players experiment with the tether to link to and open a webway gate to the boss. These methods are made to keep the players mobile and active, so they feel they had an active hand in weakening and damaging the boss, rather than just stacking damage talents and wargear. Of course, if your players are brainlets, you may want to ease on the difficulty...