The point of having a Forsaken Cloak is that you don't use any gemstones for any spells.
Am I right?
Then why worry about reducing it to 1 gemstone?
Sorry if i'm mistaken.
Ermm..
I'm not really popular with scholars but I think they use a skill called hocus-pocus and it's catalyst is 2 yellow gemstone.
Keep using that skill of course you will need alot of yellow gemstone.
And just wait until you get a side effect that causes to summon an MVP.