So far, the denizens of Blackrock only have two leaders to call their own - Rend Blackhand and General Drakkisath (with Emperor Thaurissan announced as coming soon). But what they lack in quantity they make up for in quality, with Rend being possibly the most powerful PvE leader in the game.
Rend is two minis in one - pairing the leader of the Blackrock Clan with his Drake mount, Gyth.
Rend is a 6g leader, placing him alongside Sylvanas Windrunner. You get more than six gold in value however, as Gyth is more-or-less identical to the Drake mini, and Rend himself is comparable to a Stonehoof Tauren (trading health and a small amount of damage for a cleaving attack), adding up to approximately 8g in value from him in total.
But Rend also has a passive when he’s on the field, discounting your flying minis by 1g (but not below 2g), which gives you even more efficiency. Building to take advantage of this effect is not too hard, as Harpies, Drake, and Whelp Eggs are already some of the strongest and most versatile minis in the game (with an honourable mention to Gargoyle, a powerful but slightly more narrow fourth option).
Indeed, one of the challenges of building with Rend is ensuring you still have enough map presence to secure chests and strike ranged backline minis. Pairing him with the favourites such as Defias Bandits and Quilboar can help by adding cycling options and resource contestation.
Let’s talk talents: Scale and Steel is Rend’s strongest talent, and perhaps one of the strongest in the game. It gives Rend a massive defensive boost, making the already stacked leader go that much further. Note that many, many of the most powerful ranged minis do elemental damage - Necromancer, Pyromancer, Firehammer, Ogre Mage, Safe Pilot, Jaina, Murk-eye, Skeleton Mages, Thalnos, and Sylvanas (with the Black Arrow talent).
This means against the majority of counters to Gyth, do half damage to him, massively increasing his survivability and just making it that much harder to trade evenly against him. Likewise, Rend gains Armoured when dismounting, reducing his physical damage by 50%. Melee minis are a little more evenly split in damage types than ranged, but it still adds a lot.
Flaming Soul is an interesting secondary choice. Rend uses this ability in his campaign map, and clearing all defenders (and possibly a tower) after dismounting makes countering Rend a delicate affair. Still, not as consistent as Scale and Steel and remains a niche pick.
Legionnaire is sadly a much worse option. Not only are you giving up on the more powerful alternatives, it’s also not very impressive by itself. The idea is that you get both damage dealers in play at the same time, which is nominally good. The problem is frequently this just makes it easier to clear both halves with an AoE effect, making Rend in some cases actively worse than untalented. Steer clear for now.
Rend is particularly effective against the final fight of the current campaign - Onyxia. He can clear whelps efficiently, as well as discounting Drakes to do the same. He trades fairly evenly with any minis she deploys. With Scale and Steel, Gyth can weather Onyxia’s direct assault, allowing Rend to get close enough to charge in and chop her up. This makes him an excellent choice for would-be dragonslayers.
Drakkisath is admittedly not quite as impressive as his fellow leader - but don’t count him out as Rend is a hard act to follow. He boasts enormous amounts of damage for a melee mini, amplified by his ability to increase Elemental damage taken to all nearby enemies.
He is moderately bulky, coming in just behind Cairne, but is equipped with the Resistance trait, allowing him to soak even more Elemental damage.
His primary weakness is how incredibly slow he is, tying for dead last movement speed, as well as having fairly slow attack speed. He does manage to lose a 1v1 (or 9v1) with the Chickens, so he is a leader who needs (and benefits) supporting in a larger push.
For this reason he pairs well with the Shaman, who can give him Armoured (with a talent), and supply him with the healing required to slowly make his way to and dismember his enemies.
Drak’s talents are a little more mixed compared to Rend. Chromatic Scales is quite good, keeping Drak’s supporting minis alive and still pumping. It works especially well with the Shaman, giving them both solid defenses against Elemental damage and maximizing the Shaman’s opportunities to deliver healing.
Piercing Blows is currently fairly bad. The cone of effect is too narrow to do much of anything. The silver lining is we’ve been told that updates are coming to the talent, giving it a more reasonable area of effect. Given Drak’s high damage output (and current weakness to squads), it should become a respectable option.
Lasting Legacy is an interesting third option. In the right build, it can be exploited to maximize the amount of Gold-Into-Elemental damage that can be delivered to the target. I wouldn’t currently pick it over Chromatic Scales in too many situations, but it’s one worth keeping an eye on. Delivering a final Blizzard or Deep Breath might turn out to be game winning.