Don't know if there are many illusions spells in the mix, but just a few suggestions:

1) Overland spell: Illusion army: make an army seem more significant unless you have actual combat with them

2) Overland spell: Illusion resource: makes a resource appear unless your units get really close

3) Overland spell: Illusion fog: makes it harder to see what's going on inside another Sovereign's zone

4) Overland spell: Illusion direction: makes a foreign army confused and may lead them to move in a mistaken direction

5) Combat spell: Illusion unit: Makes a fake unit which {only stays until hit, may reduce morale of opponents, may cause opponent to flee, etc.}

You get the idea.