|Neil Spicer RPG Superstar 2009, RPG Superstar Judgernaut, Contributor|
Not familiar with the mythic rules at all, any concrete advice?
Mythic Monsters for Ydersius. The easiest thing to do would be to give him the Invincible simple template. That will take him to CR 20, AC 39, give him DR 10/epic, Resist 15 vs. all forms of energy beyond those he already has, grants him 20 mythic bonus hit points, as well as the ability to block attacks and make a second save against ongoing effects...although, I'd probably recommend dropping the second save ability and trading it out so he can gain dual initiative and take more actions per round. Since he's already getting +36 on his attacks (and +31 with his tail slap, which can grab and constrict), your melee PCs should have their hands full for quite awhile with him.
Mythic Hierophant for Vyr-Azul. You should probably go a little easier with this one, because if you make Vyr-Azul into an absolute mythic powerhouse, the PCs will struggle to handle Ydersius when he crawls out of the Chasm of Retreat (at C9). At most, two mythic tiers as a hierophant should be sufficient. It'll grant him amazing initiative so he can take multiple actions per round (which should enable him to make an attack in melee and cast a spell). He'll also be harder to kill and you can either grant his animal companion, Qestl, some significant melee capability with beast's fury and mythic companion, or boost Vyr-Azul's spellcasting power with recalled blessing or inspired spell and then give him the flexible counterspell path ability to nullify a PC spellcaster. Or, a better option might be to give him a legendary item or mythic spellcasting from the universal path abilities, thereby ratcheting up his options in combat. If you go with mythic spellcasting, you might consider giving him access to mythic dimensional lock so he can prevent the PCs from using teleport so easily...all while leaving his own teleportation spell-like abilities unaffected (i.e., if the PCs want to "scry and fry" as they say, make sure Vyr-Azul can do the same...and bring Ydersius along with him).
Hope that helps,