An option to toggle certain skulls that change specific game-play mechanics (like in Halo firefight) that make the game harder but reward you for completing their criteria. This could be linked to the bestiary, like for instance, if you discover all enemies with a shield you unlock the shield skull and etc. Some examples of these could be:
- Enemy shields now have double base health but every time you destroy one your shield mods are boosted by 1%.
- Every time you destroy a champion enemy a random filter is applied to the screen (like grey-scale, monotone, haze, increase/decrease in contrast, screen flip) and for every filter applied your global damage is boosted by 1%.
- You forfeit the 3 starting gear mod pools at the beginning but any gear you pick up is boosted.
- Screen wrapping is no longer mirrored, it becomes random for both the player and enemies.
- Enemies can now pick up boosts but destroying a boosted enemy boosts your base stats for the remainder of the run.