Chemical Composition of Creeper?

[Randomgold]

All three games refer to a "dark reality" that turned the Loki evil when they looked at it.

Maybe it just refers to a truth of some kind?  You know, as in they discovered (saw) some 'truth' of their life and it became the "dark reality" that they saw into.  So not really a physical reality, but a symbolic one? 

[Asbestos]

Symbolism is for wusses and English teachers. The Loki presumably have a hive mind. When they looked into an eldritch universe, the hive mind went mad and turned evil and omnicidal.

[MagneticDuck]

All three games refer to a "dark reality" that turned the Loki evil when they looked at it.

The Arc Eternal ending resolved that story arc brilliantly :P