Lowest level challenge?!

[Zechnophobe]

Depending on Class, one stack green, one stack red, works pretty well vs Zilgadis. I think you are forgetting that the royal griffons have no no-retaliation way to deal damage to Ziggy, so they also need to worry about physical damage.

Also, we can very likely take all the battles on Debir and scarlet without giving us any extra levels at the end, so yes, they should either be saved to unlock runes, or used early for Grand Strategy.