I'll be taking the first step this week in a project to create what will hopefully be a centerpiece for my guard army: 8 rough riders on giant boars. I figure since the Tiefwalders are more of a forest/jungle theme, the big swine would be more appropriate than horses. I've gathered a selection of bits for conversions: their hunting lances will be wooden staves with combat knives and grenade packs tied on one end, and the vet sergeant will have some choice trophies - ork, genestealer, chaos marine helmet - to help him stand out. The biggest challenge will be actually mounting the men on the boars. I don't actually have any in front of me yet, but from pictures it looks like the ork rider legs seem a little too big for a catachan body, arms, and head. I may have to resort to whittling in the end.
For all the work it will take me, the value of the unit is honestly debatable. They'll be highly fragile one trick ponies (or piggies, as it were), but they only cost 94 points and they're good for a far-reaching counterassault, killing 4-5 MEQs on the charge before they get swung back on. They're basically one more finger in the leaking dam, hopefully granting a bit more time for the big guns to do their work. Overall though they're more about bringing in a unique unit and giving me some fun modelling opportunities.
To work them into my current list, I'll have to consolidate two of the sentinels into a single unit and drop one of the chimeras; no big whoop. There's no way I'm giving up that hellhound. He's just too sweet a killer and many seem to fear him more than the demolisher.