Converting epic creatures to Pathfinder

[Selion]

My players asked me to continue an old campaign.
I want to give big bad end game guys with actual stats.
Fisrt one is a phane
https://www.dandwiki.com/wiki/SRD:Phane
Stats seems pretty consistent with Pathfinder ruleset, but maybe it needs some icing on top, maybe using mythic levels. Do you think CR 25 is still a good measure of its power sets even in Pathfinder? Consider he could be the last battle PCs would fight, depending on their decisions.
The other one is a white dragon demigod, 3000 years old. I need for him 9th level spells, is there a way to improve a white great wyrm stats? This is not an enemy PCs are suppose to fight and in general he is not hostile to them. He just has something the PCs need, so a battle is possible, but not recommended. His CR ideally should be from 25 to 30. I want to give him 10 mythic tiers, but it's not mandatory.
PS: PCs are not in the final saga, they are currently level 12-13, so there is still a lot of adventuring between them and these beasts

[Selion]

Uhm, for the dragon I just realized that 10 mythic tiers raise the CR by 5, a great wyrm red dragon has already CR 22, so if i want a CR 27 dragon i just need mythic tiers and use the red dragon stats to represent a white dragon.

[the_david]

You could give the dragon sorcerer levels instead. You could indeed alter the red dragon, or you could use the stats for the silver dragon. They've got the same challenge rating.

As for the phane, you can there's a monster statistics by CR table in the Bestiary, or you could use the quick monster creation rules in Pathfinder Unchained.

[Efrate]

ELH has a way to advance dragons with more racial hd which gives more benefits, up to and including a new size category in colossal +

[the_david]

ELH has a way to advance dragons with more racial hd which gives more benefits, up to and including a new size category in colossal +
Except that he wants to use Pathfinder rules, and giving a dragon is a perfect way to do this. Even if he'd give a great wyrm white dragon 9 mythic ranks it would be a CR22 or 23. It would have 10 mythic abilities. 3 of them would need to be used for Divine Source so it can grand up to 9th level spells to clerics. It could also take simple arcane casting to be able to cast some 7th, 8th and 9th level spells. That's all it would take for the dragon to be able to do what it should, except that its CR should be at least 2 or 3 points higher.
Honestly, I love the solution of reskinning another type of dragon for this. Actually, I take that back. Instead of a white dragon it could be a tarnished silver dragon. It's just that people keep seeing an evil frost dragon so it must be evil, right?