Dirtamancy + croakamancy: pestilence - destroy all crops in a hex and prevent more from being grown there. Particularly useful if the "Charlie needs heroine buds" theory holds water...
Dirtamancy + foolamancy: make a hex appear to be of a different terrain type. Upgrade a city to be permanently veiled.
Dirtamancy + dollamancy: animate a city and have it start attacking the inhabitants/make it able to defend itself against attackers. Create building-sized golems (giant mechas!). Rapidly erect gstring-secure structures.
Dollamancy + croakamancy: magic item that stores "charges" of decryption. Makes Wanda much less vulnerable in the field. Combine this with the 'pew' death ray and you have an instant "convert enemy to ally" button.
Dollamancy + foolamancy: magic item veils all units in a hex, and projects an image of those units in a nearby hex.
Foolamancy + croakamancy: create uncroaked/decrypted that look like a living unit. Use them as decoys or spies.
Shockamancy + thinkamancy: Rule 34. Attack with shockamancy via thinkagram
I feel like one way to amplify the power of linkups is to use them for fabrication. Ordinarily there's only so much you can do in a turn with linkups. But spend a dozen turns using linkups to craft, and suddenly you've flooded your side with game-breaking magical items. Also, if the GMTTA can be convinced it's worth their while, Parson could use all their leftover juice that the end of a turn for additional crafting.