My knowledge of StarCraft lore is perhaps best described as "minimal" but there's a short Hotline Bling reference in the Dehaka introduction video so now I have "You used to call me through the Overmind..." stuck in my head as a lyric. It kind of fits as Dehaka's whole deal is that he stayed home on the Zerg planet and is an individual not part of a swarm but I'm not sure that the Overmind would have ever called him because he doesn't have a psionic connection which I assume you need for zerg brain broadband and booty calls from the Overmind or whatever.
Anyway, here's how the hero works:
So he's a melee warrior whose high mobility should come in useful for ganking or for setting up pick-off kills. He can also regenerate health and do area of effect damage making him a massive pain in the butt during team fights.
Here are his abilities:
D - Collect Essence
This is the thing that's unique to him. He gains a resource called Essence when enemies die. 10 Essence from takedowns on enemy heroes and two from nearby minion deaths. If you activate this ability he'll heal over a five second period in accordance with how much Essence you've collected. So essentially he needs to keep participating in kills to become this highly sustainable presence in fights.
Q - Drag
This is a kind of angry chameleon skill. Dehaka shoots his tongue out damaging the target enemy and then dragging them with him briefly. I feel like this could be a good initiation tool but you can also use it to drag heroes within range of structures that will attack them, or to yank them out of position in fights.
W - Dark Swarm
This is the area of effect ability. He has a little swarm around him that deals damage. You can actually cast it while using Drag or Burrow so that'll be annoying to deal with. He's also able to walk through units while using it so could feasibly just wander over to squishy supports.
E - Burrow
Dehaka goes underground, entering Stasis and becoming Invulnerable for a couple of seconds - essentially he goes off the map briefly and thus can avoid particular spells or play for a bit of extra time in case a teammate is needed to come in and save him.
R - Isolation
With this you can silence and slow an enemy, letting you take important targets down as they flee or taking particular problem heroes out a fight for a few seconds by stopping them from casting their abilities.
R - Adaptation
This one is more about survivability. You have a five second delay and then you heal for 60% of the damage you took during that five seconds. So basically it punishes people for whaling on you during a fight.
Z - Brushstalker
This is usually the button you press to mount your steed and get more movement speed but I guess zerg and horses are natural enemies or something? They used to call zerg on the horsephone...? Anyway, INSTEAD of a horse you have Brushstalker. Brushstalker lets you create a tunnel and travel to any patch of brush on the map (or vents if you're on a vent map). So you can basically turn up on the other side of the map and be a right pain.
I just tried Dehaka out in that test mode they have in the in-game shop and the cooldown on Dark Swarm feels incredibly low. Obviously it drains your mana if you keep casting it but then you just teleport back to base and use Brushstalker to get back into lane so you can refresh mana with minimal disruption.
The patch which brought Dehaka also brings Lost Cavern, which is the single lane map. It's in the Custom Games section if you fancy that.