Pre-Notes:
*Passing in this context means a parent with the feature passing it onto cubs
*Combo Bases are currently Cairngorm, Madagascar, Citrine, and Qahir
*I am referring to the bases that can create a Combo Base as Combo "Components" because I couldn't think of a better word rip
*Amazing guide by Berenos with Combo Base info

Combo Bases are a really exciting feature, and a great challenge for base-breeders. I really enjoy checking to see if my in-heat females are one of the combination Components, and finding a matching stud~

If you have a Combo Base lion, in order for it to pass you have to breed it to one of the Components: eg, a Cairngorm x cele, ice, sidereal, sky, cocoa, ethereal, pearl, or slate. Any of these pairings have a chance at a Cairngorm cub.

This is all and well, but.... what about Cairngorm x Cairngorm? Currently, this pairing cannot pass Cairngorm. Since both are the Combo Base, I think this breeding pair should be able to pass on their base.

My suggestion is:
If you breed a Combo Base to itself, it should be able to pass said Combo Base

I am unsure about the idea of breeding Combo Bases to a different Combo Base, eg Cairngorm x Madagascar. Since Madagascar isn't made up from the same Components as Cairngorm, I can see why they shouldn't be able to pass a Combo from this pairing.

Would love to hear your thoughts!