Boomhowler would work well with Ashlynn.... if she'd have him. Sadly; he won't work for her (or vice versa).
The dope on Epic Magnus says he has Blur. This will make the Trollkin a much more attractive option if he can cast it on them.
Luckily for you; there's a starter for Mercs that will use the trolls (twice in fact) which is Magnus and Gorten. The Dwarf is slightly less competitive of the two as the Driller is a lot of points for a very slow sledgehammer. That being said he makes a very powerful reserve unit and I ususally marshall him with High Shields to act as a counterattack. Gorten needs to make the most of his 5 Focus and if you marshall boost the gripper attack then the Driller will autohit with his drill.
A Gorten box, Herne and Johnne, the Highshields box and Boomhowler box will give you 497
Herne and Johnne
This is a shooting list. Advance in the first turn and set up a wall of stone for your gunbunnies to hide behind, then blast everything as it comes into range. Feat to move troops back so you can blast them again. When combat is finally joined Boomhowler, the Driller and Gorten can all take out hard targets fairly easily. Cast Rock Wall and Ground and upkeep that most of the game, which will give you 3 focus per turn for your Bunnies.
On the other side we have Magnus... with some of the BEST warjacks out there (his custom ones). The Mangler and Renegade are both awesome for their points (especially the renegade!).
With a Magnus Box, Boomhowler Box, Alexia box, Eiryss and Rupert you get 496pts.
Talon (I'd suggest getting another Renegade and using it instead, you won't go over 500)
Rupert (as backup)
This list is a bit more finicky and will need to be agressive and passive at the same time. Pick your fights and use Magnus' feat to you out of trouble. Renegades work well in a pair, one bombing and the other shredding. You've got no defence against KD and Stationary in this army (apart from Feign Death on Magnus... which won't stop freezing unfortunately) so you'll need to combine units to support each other. Use Eiryss to kill unit leaders to make enemy infantry less maneuverable. Alexia can then handle pretty much any unit with attrition by raising their casualties. You can blur the Trolls with Magnus to keep them alive. Rupert will make Boomhowler more survivable with Cloak of mists. Running terror causing trollkin into base to base can be deadly as well if you've managed to nuke the unit leader already with Eiryss as you'll get a ton of free strikes.
Epic Magnus will likely be a good choice in 750 once he's out. As long as he retains spell that can help more than his battlegroup!
There's my 0.02. I use Mules and Ashlynn mostly myself, but I've dabbled in Gorten and Magnus. Good luck!