Until the release of the new Chaos marine plastics a few years ago, the 40k Chaos army was looking pretty long in the tooth - and not in a wolf-like, fanged way. The new marines are very nice, but there are still some ancient and rather ropey models in the range that need updating: most notably, the Berserkers of Khorne.
Chaos bikes are another seriously ancient unit. I reckon they current models have been around since 1998 or so, and they look chunky and dull (not that the old Space Marine bikes are much better). Anyhow, I had some bikes knocking around from a very old set called Dark Vengeance (as opposed to Happy Vengeance or Merry Vendetta), which I'd started converting ages ago and then abandoned. I thought that I'd have a go at converting them into something more chaotic and more interesting.
All the bikers got new heads. The first got a lot of spikes growing out of his bike, along with some strange bony protrusions. I decided that all three of the bikers would have unwholesome tubes connecting them to their vehicles, perhaps where they were starting to merge with their rides.
The second biker had a sort of weird pump fixed to his bike instead of a backpack, as well as a big skull to act as a sort of windscreen and some manky fleshy stuff coming out of his chest. Nice.
The third biker is probably their leader. He's got a daemonette of Slaanesh riding pillion.
Lovely! They'll be able to raise some hell in the name of Chaos, assuming that quarantine ever lifts. Chaos grows ever stronger (and faster)!