[Hrum]

It would be interesting to hear if anyone has ever used either of those spells in MP.

Aside from the question of whether they're considered a worthwhile use of gems, my suspicion is that neither global gets used very often in MP because it's a declaration of war / cancelation of NAPs with all the other players in the game, same as with Burden of Time or Astral Corruption.

OTOH it might be kind of entertaining to have both Astral Corruption and The Kindly Ones in effect at the same time. No one is safe! I wonder if that would make an interesting apocalyptic SP scenario - both of those in effect from turn 1. If that isn't hellish enough, you could add The Wild Hunt and BoT.