I know I'm a bit late but I was really enjoying Thunder Junction as a drafting experience, even if I found it a bit muddled from a lore perspective.
But I wanted to ask the question if Jaspar, Vaalin, Dolores, Dancing-Hands, Zarunpel and Ranek had there own Mount what would it be?
Alrighty, let's start with the really easy ones, the ones I already made cards for before this ask...
For Zarunpel, her Mount would obviously be her mount, Velumbra. She's a magical panther from Urborg that lives within Zarunpel's shadow when she isn't stalking around in the real world, and was granted to her as a token of friendship by the Soul of Windgrace after she did him a service helping his people and him personally with an off-plane errand, during the Dominaria United period.
For Jaspar, something less specific but I do have this design for a mount for him. His magic allows him to call upon the echoes of life past imbued into parts of creatures for various magical effects. This is him using a discarded antler of some form of elk to summon a spirit version of it to carry him around. Since antlers are shed periodically and don't stay with an animal for their whole life, their echoes are fainter than what he may obtain from most bones or other parts. As a result, they stop working with his magic after some time or intense use like this. Thankfully, finding "fresh" antlers to restock is also pretty easy.
That's it for the cards I already have figured out (at least for the list given).
Dancing-Hands doesn't use a mount very often, but in the past he's been seen on the back of an origami horse animated by his magic when he first arrived on Amonkhet's desert, a few years back at this point.
Dolores and Ranek are less likely to have mounts these days; Dolores's wings mean flight is more often a faster option, and flying mounts that can keep up are a hassle. Ranek travels in his Stormplate, as much mech as it is armor, and even if he supplemented that with other forms of transport, it'd more likely be a vehicle of some sort than a mount.
Vaalin... I genuinely don't know. We don't see enough underwater content to have a wide range of options there, and given he evolves on land too, would have to be amphibious, but he's not exactly riding around a lot either. Vodalians have seahorse mounts, but I doubt Vaalin could get one of these with his status, and he's not Vodalian proper either. Could see him riding a drake through the air!