The idea is that Tellus is Rune's shield oath and Lux is it's sword oath, and unda could be a cool down or a stackable buff depending on how it balances out. It would be cool that if you have three undas on an ally you can use an ability to expend them and heal them

And honestly it was a bit hard for me to come up with good debuffs that weren't completely redundant or too op XD