I'm analyzing 
The Ethereal Diamond meta is slightly different from what I play against in Mythic. The lines are the same, but I'm expecting tighter play from the opponent and better cards like Highborn Knight or Pyramid Warden. Not to say that my lines I suggest are the best ones to make.
Strategy
HRD can win against Aggro Light by getting ahead early with good trades through Armor Lurker, Pyramid Warden, and Makeshift Shiv and denying your opponent board control, rendering their buffs useless. Or you can rush them with hidden creatures and slow them down with Stoneskin Poison or Umber Arrow. Aggro Light doesn't have an answer to Shadow of Lethenon, and drawing it lean you towards the rush plan, especially if you draw Dark Knives. It's hard to tell what strategy to go for, as the game plan evolves over time with cards drawn and the opponent's plays.
Light going wide can be rough. Knowing your opponent's deck and deciding when to control board or rush face is a key part of HRD. If they run Protective Benediction, the rush plan is risky since its hard to get through a wide board of protected and frontline creatures.
Mulligan
Mulling away the 4 drops is right. I would have mulled a Looter too. I'm not happy or sad to see Looter; it's kind of mid, dealing 2 damage, then die and draw a card. Just low impact when I could look for Armoer Lurker, Makeshift Shiv, or Umber Arrow to control the board against what is probably Aggro Light with the Summon GP.
I'm not scared of Light's Levy since I'll probably trade off my guys to control the board early instead of pushing face.
Turn 1
Playing Switch Duelist to save pip is a line you can take. It helps you get out a 4 drop earlier but you're lighter on those. Occasionally, you can go pip a 4 drop on turn 3, followed up by a buff and hide it on turn 4. You get in 7 damage on turn 4 and every turn after by hiding your guy repeatedly in they don't have frontlines. Stacking one big guy and hiding it repeatedly is a wincon against decks that can't clear it.
kstreet playing Looter is fine too, trade it off and dig for cards.
One Dryder Sailweaver is slow from Aggro Light. I'm expecting the opponent have a 3-drop like Militant Theist or Light's Levy.
Turn 2
I would have traded Looter and see what I drew, then played Looter or something else. Fight for board early and slow the opponent down.
I don't like playing knife on Looter here. You would like to save knife when you can hide the guy after and get more hits in with the buff. I'm not keen on rushing face with this hand either, not a lot of pressure available in hand.
The opponent ordering on the Looter is odd. Order means they'll have a hard time killing it and will likely eat 5 more damage or have it make a good trade.
Turn 3
There's a hard choice to make here. You could ignore the board and attack face with Duelist, then lock up their board with barrels. They can't clear they own board and will be stuck with a few small guys. If they don't have any buffs, you'll be in a great position as they'll float 3 mana. If they do have buffs, it's not the worst as Radiant Dawn isn't that strong on 3 guys, and the barrels will gum up their board another turn. And you have Blade of the Whiteplain to play against a Benediction buffed board. You're not threating that much damage on board, so I'm not sure how much locking their board with barrels will help. Or you could trade Duelist and play Looter, slow them down a bit while you try to find a threat.
Fighting for board is probably better since you have Blade of the Whiteplain in hand, and getting that down against a small board is great, since Light has a tough time dealing with it.
I don't like trading and playing barrels. You don't lock their board by trading, nor will you develop your own board. Barrels is only useful for stopping them from playing creatures with a full board or getting in the last points of damage.
Lysander's Spear is hit or miss against HRD. Sometimes the tempo loss is too much and you can rush them down. Other times a big frontline slows you down. You rarely win a board game against Spear unless you are well ahead or they brick since a +2/+2 buff almost every turn is hard to deal with.
Turn 4
You could have gone face with the Looter instead of trading with Informant and hope to top deck hidden creatures to race. But you don't have the pressure in hand for it to be worth taking this line. Trying to get in 20 face damage in this situation is rough.
On the other hand, it's not easy catching up on board against Spear either, but your opponent is low on cards in hand, and the Blades can turn it around. So trading off the Looter is better.
I'm kind of happy to see them play Canonize. They don't develop their board and Stoneskin Poison slows them down.
Turn 5
kstreet takes the only good line, slow the opponent down with Stoneskin and develop his board with Pietro.
The opponent misplays by buffing Vesper with Spear and Janissary and probably lost the game from it. I would have buffed the Acolyte and Janissary instead for a 6/6, 4/4, and 3/3 board instead of 9/9 and two 2/2s. The Vesper is already a threat and buffing it more doesn't help clear the board or push more face damage. Buffing the others so they won't get traded would have been a lot better, especially when they can see 2 strength creatures on your board.
Turn 6/ 5.5 Mana
Marcella is a huge draw because she gives you deadly Skulkers to clear the Vesper. Clear with Looter and another creature to keep your Skulkers around to kill Vesper. Using GP on Vesper doesn't do anything useful; there's no difference between 8 or 9hp here. Hiding your Marcella might have been better since they can't kill it, and you won't have to deal with deadly Skulkers, letting you play Blade easily. Although it's not terrible with Umber in hand. Another line would be trading Pietro into a 2/2 and using GP to finish it.
I think trading Marcella was the right play for the opponent, going against what kstreet says. If Vesper had gone face, it leaves kstreet with only 10hp. They would get their board cleared after, making it difficult for them to make a comeback. Since Light had no reach, they would not be able to close out the game. Killing Marcella fights for board, which is the only thing Light can do. It forces kstreet to have removal for the Skulkers and sets up a board buff.
Turn 7/ 6 Mana
kstreet clears most of the board using gp, Umber, and trading creatures.
If kstreet hidden Marcella, then on this turn, assuming the opponent traded the Trial Spirit with Vesper for board control, would have Pietro, 3/2 Marcella and a deadly Skulker vs Vesper, Exortionist, Militant, and a buffed Vicar. kstreet could have cleared Vesper with the Skulker, pop protected with Pietro, use Umber and Dark Kniives on the Militant to trade Vicar, then you can trade Extortionist with Marcella and buff her with Rune of Strength, or use GP on the Extortionist. The opponent's board would have be cleared but kstreet would have to deal with Skulkers eventually. I'm not sure if this would have been better.
Chaining of the Gods and Enraged Ally is a manageable board from the opponent.
Turn 8/ 6.5 Mana
Blade showing why it's $300 with its removal, draw, and a body, crazy. Top-decking Shiv is great too, allowing kstreet clear the Extortionist.
The opponent is on their last breath. Buffing the 1/1 with Spear stops it from getting pinged or shived, but it walks right into the second Blade.
Turn 9/ 7 Mana
The second Blade comes down and breaks the opponent's spirit.
The game turned around the turn the opponent went tall on Vesper, letting kstreet regain board control. The Blades and Shiv were the nail in the coffin for the opponent. Sloppy plays from the opponent gave kstreet the opportunity to catch up.
