image from Privateer Press
Nothing special here. Fury 6 is average and RAT 7 is solid for his guns.
Black Penny is a pretty cool thing to have for a guy packing two magical hand cannons and access to Snipe. Evasive, Swift Hunter, and Pathfinder will allow him to be all over the board to make his shots count. Gunfighter means he won't be totally shut down by being engaged.
This is where the fun is.
Quicken! SPD 8 Fennblades? SPD 9 Long Riders? Heck, even SPD 7 Champions! Or, what about SPD 6 Mulg?!
As if two hand cannons with Black Penny weren't good enough for spot removal, enter Magic Bullet. Now not even Stealth can keep those pesky solos safe!
As if Quicken weren't enough to get Jarl's army moving, enter Tactical Supremacy. I'm thinking that Champs with Skaldi can charge forward, use Follow Up to kill more stuff, and then consolidate using this spell to get their defensive bonuses.
Weald Secrets is another movement buff for Jarl's infantry and saves the Fellcaller from having to give a unit Pathfinder.
Three of these spells are upkeeps and Jarl is going to want Far Strike most turns so I'm thinking he'll be a little short on Fury for transfers.
The spoilers are a little unclear about this but it sounds like he'll get to place at least four 4" AOE cloud effects in his control area. They don't block friendly LOS and friendly models get Pathfinder and can move through things while they're in the clouds. There is also some rumored penalty to enemy models that move through them.
It sounds like a cool board control feat to me that can help zone off sections of the table or allow a free-ish turn of movement.
Jarl sounds like a very good infantry support warlock, especially in the movement phase. His guns are nasty against infantry and solos but he won't be able to seal the deal against enemy 'casters alone. Mostly he looks like a lot of fun (and what a model!).