Rexxar is perhaps one of the most diverse heroes who can be built in different ways for different roles and playstyles. And he's the hardest Warrior hero to play so he requires lots of practice to be even decent at him. One of the builds where he shines is his jungle build. As the name may suggest with this build Rexxar can capture mercenary camps, solo bosses and clear minion waves very fast and effectively. This build greatly buffs Misha to take less damage and deal more damage to mercenaries and lane minions. And Spirit Swoop will clear mercenary camps and minion waves a lot faster.

However, I would not recommend this build if you're the only Warrior in your team. This build, and hero in general, truly shines in double-Warrior team compositions. If your team lacks another Warrior to engage and tank most of the incoming damage from enemies, you may want to consider going for this build, no matter how good the map might be for that.

And while this build is not the most effective or helpful in team fights Misha, Charge!'s multi stun is still very valuable and can win team fights. And Misha can still work well as an off-tank too. So don't neglect your team and team fights for the favor of mercenary camps or even boss(es).

Now let's look at the overall build more closely:

Tier 1
Hunter-Gatherer Since you're going to be killing lots of mercenaries and enemy lane minions you're bound to be getting lots of Health Globes and thus your health regeneration is going to be increased a lot, giving you more sustainability. Against bosses especially this is rather important to have.

Flare is another option and a good talent to have no matter what kind of build you're going for as Rexxar if the enemy team has stealth heroes like Nova and/or Zeratul and you're not too good at seeing them through their stealth cloaks yet. You can use it near bosses or normal mercenary camps on the enemy's side just in case so you can see them if they're trying to ambush you. And of course at the objectives to help your team to spot them more easily, thus making them more vulnerable.

Tier 2
For this build Easy Prey is simply a must-have talent. You want to clear out mercenaries, bosses and lane minions as fast as possible so this is obviously the best talent for that.

Tier 3
Bird of Prey. Another must-have talent in this build. This will deal tons of damage to mercenaries and bosses and clears minion waves extremely fast. One shots basically.

Tier 4
To take down bosses faster Bestial Wrath is a very good talent. This is when you start to go for bosses when the time is right (like when 2-3 enemy heroes are dead or when they're too busy with the rest of your team). You can take down bosses even if you went with Unleash the Boars but you really want to take down the boss as fast as possible. You don't want the enemy to notice and stop you in time and possibly steal the boss from you after all.

Tier 5
Wildfire Bear Simply to deal more damage to everything around Misha, including mercenaries, bosses and lane minions to take them down faster. Plus it's a good way to reveal stealth heroes simply by sending Misha right next to them if you can see them through their stealth cloaks.

Tier 6
Not very good talents for this specific build in this tier but I would go for Feign Death simply because it's very handy and can save your life if you just remember to use it at right times (like to counter Nova's Triple Tap or Precision Strike and Kael'thas's Pyroblast etc.).

Tier 7
Frenzy of Kalimdor is perhaps the best talent for this build in this tier although Spirit Bond is not too bad either. With this talent you simply deal slightly more damage and thus can take down bosses slightly faster. But only slightly.

The best maps for Jungle Rexxar build are obviously the ones with lots of mercenaries and boss(es). The best one of them all being Cursed Hollow with lots of mercenaries and two bosses. And it's a large map too so you can take out mercenaries and your own boss while being rather safe compared to other maps where the boss is at the middle of the map. But don't let this drop your guard down. If the enemy team is smart and they look at your talents they will realize what you're trying to do in this match and they'll scout the boss areas to see if you're trying to solo bosses. So capture bosses when 2-3 of the enemy heroes are dead or when they're too busy defending their structures from your team while being cursed. And don't ignore the objectives and teamfights, of course. Not only on this map but any map, really. Your teammates will appreciate that. You can go and take mercenaries later.

Tomb of the Spider Queen: Another very good map for Jungle Rexxar. But not specifically for the boss, although it helps, or mercenary camps because there's only 3 of them and one of them is on the enemy's side where you can't get to safely for quite a while. But this build is very effective against the Webweaver waves. They will melt before this build and that is of course very annoying for the enemy team to deal with. So this is more like a counter pick against the Webweavers rather than specifically for capturing merc camps. And because the map is rather small going for the boss is very risky so I highly recommend you to go for the boss after a good team fight where most of the enemy heroes died. Don't go for it just before your team's next turn in, though. The enemy will notice that the boss is still active and realize that you, or someone else in your team, is doing the boss and will most definitely come and stop you. Plus this is a rather small map with 3 lanes so farming minion lanes for health globes and of course for spider butts (gems) and just to help your minions to push is a lot easier.

Blackheart's Bay: Lots of mercenaries, a boss and the pirate camps with coins (not like they're hard to take down anyway, though). Since you'll be soloing the camps for the most part while the rest of your team focuses on pressuring the enemy team on lanes you will most likely have quite a lot of coins. Which is why you must be very careful when going for the boss. Not only is it at the middle of the map where the enemy can come and surprise you at any time but if you get caught and die to enemy hero(es) losing lots of coins in the process you and your team are f*cked. Just keep that in mind and try to return coins as frequently as you can to avoid any big coin losses.

Sky Temple: Same as Blackheart's Bay but without having to worry about coins. However the boss in this map is at even more exposed area than Blackheart's Bay's boss so the risk of getting found out and ambushed is even higher. So here only go for the boss when most of the enemy team is dead. And again; help with the objectives whenever you can. Mercenaries, and especially the boss, can wait (unless of course most of the enemy team is dead and your help at the temples is not required).

Towers of Doom: I have played only one game on this map as Rexxar so I can't say for certain whether this is a good build for this map yet. But the boss, Headless Horseman, seems like a big pain in the *** to deal with even as Rexxar. And it looks like a map where the risk of getting ambushed is very high. But I need to play more games there to be certain so I'll update this part once I have come to a conclusion.

On the other maps I suggest you build Rexxar as more team-fight focused. The lack of lots of mercenary camps, and/or boss and having only two lanes in some of them so even farming health globes is not very effective on some of the other remaining maps thus making this build way less effective and meaningful on them. Well, Haunted Mines may be an exception because with this build you can clear the undead mobs with skulls fast (although so can many other heroes) but most of all you can kill the enemy team's golem much faster with Spirit Swoop. Not 100% sure if Easy Prey works on bosses. But if it works on Webweavers, it should work on golems too. But, it's up to you whether trying it out on that map is worth it if you happen to end up there as Rexxar in Quick Match (if the map ever comes back to Quick Match, that is).