I played 103 games in Legend where my mmr was such that I faced Diamond 5 - 1 players. This was done to get an idea of how this deck would perform in the Diamond 5-1 range. The results are a 61% overall winrate.

Matchups Guide

Demon Hunter - Mostly odd demon hunters, you can win if you gain early board control. Feels slightly favored.

Druid - A lot of slow combo druids that you can burst down before they get their combo going, be careful about hero powering and playing small elementals because of Spreading Plague. Very favored. Also faced a few aggro druids, if you can get early board control you win but it feels slightly unfavored.

Hunter - Mostly even hunters and faced an odd hunter, it's slightly favored because the wins were more decisive than the losses. You need to try to burst them down before they do because they will definitely be doing a lot of damage and you lack healing and taunts.

Mage - Some combo mages, feels slightly unfavored because they keep freezing your board and combo before you can kill them. Make sure not to play too many small minions on the board because of their freezes so you can be able to play minions with direct damage face. Secret mages were a favored matchup, you need to get on board early and deny them their draw from Rigged Faire Game and keep pushing direct face damage from minions, battlecries, and weapons. It's a race, they will win in the long term but you can often burst them down and win even if they eventually regain board control. The last was 2 games of reno mage, which feels favored as won despite them having Zephrys, Kazakus, and Reno. You need to have board control and push face.

Paladin - Very favored matchup, mostly odd paladins and a few handbuffs. You need to have board control for odd paladin and try to push face as fast as possible for handbuff paladin because they can eventually otk you. 

Priest - Very unfavored against big priests, which were the majority of this class. They have too many taunt walls and removal and healing, but if you have Lilypad Lurker you can sometimes manage to win. Reno priest is slightly unfavored due to their plentiful removals but sometimes you can burst them down over a couple turns if they don't have Reno.

Rogue - Mostly kingsbane rogues, slightly unfavored because they will keep hitting face with their weapon and you have no taunts. You need to have early board control and rush face to win.

Shaman - Reno Shaman is favored, you can often win even after they play Reno. Try to avoid overcommiting on board so you have more waves after their board clears. Murloc shaman is even, whoever gets early board control will win.

Warlock - Very favored vs Renolock, won multiple times after they played Reno and other cards like Zephrys just because other than Reno they lack heal, and you have a lot of burst damage. Furthermore you can use Lilypad Lurker to hex their big demons. Discard warlock was another common matchup which is slightly favored, just focus on getting board control and eventually bursting them down as they have no heal. Finally, darkglare warlock is even as they will probably get board control in midgame with giants but if you can do enough damage early you can burst them down later.

Warrior - Control warrior is even, don't overcommit on board but try to keep pushing face before you run out of cards. For pirate warrior it's also even and mostly about whoever gets early board control.

Card Stats

This shows the mulligan winrate, percent of times kept in mulligan, drawn winrate, and played winrate for all the cards in the deck. It's sorted by played winrate. You can see that Brann Bronzebeard is in this, but after seeing how poorly he performed I replaced him for a second copy of Cagematch Custodian. This is interesting to see which cards perform well in certain cases. Something like Fire Fly has a great mulligan winrate but much lower played winrate implying it's really good in the mulligan but is bad as a topdeck later in the game.

Deck MVP: Primal Dungeoneer

I just started using hsreplay stats and am going to be giving deck MVP to whichever card has the highest played winrate over 100 game for each future deck I post. The very first deck MVP is for Elemental Shaman and is Primal Dungeoneer, having a played winrate of 71.7%.

Mulligan Guide

Mulligan for Primal Dungeoneer, Cagematch Custodian, Fire Fly, Wailing Vapor, and Kindling Elemental. Some other cards are situational picks depending on the cards in your opening such as Kazakus, Golem Shaper, Arid Stormer, and Earthen Might.

Conclusion

In general the key to playing this deck well is to know when to focus on pushing face with your plentiful burst damage and give up board control as opposed to using your minions and damage battlecries to keep board control. It depends on the specific situation you face but if you are against a class with no healing but a lot of board clears then pushing face over time will be more likely to give you a win than trying to maintain a board. This deck has a very good winrate in the Diamond 5 - 1 range so it seems possible to get Legend with it. It has a lot of new cards (11 / 30 cards are from the latest Barrens expansion) and is fun to play if you like a midrange deck where you have a lot of burst potential.

Here are two replays which demonstrate different strengths of this deck:

1. Winning on turn 4 with an aggressive start. https://hsreplay.net/replay/UExdG6QChCaFaHoB7b4nwV

2. Winning over time against a Renolock that played Reno. https://hsreplay.net/replay/VrEbf6Nxk6Lfab7ERQphQ6

If you have any questions or comments write them below.