Here's some information you need that's not in the screenshot:

All minions in my hand have 1/ 1 from Keleseth

All secrets came from Zul'jin. Because of this we know what all the secrets are:

• Venomstrike Trap
• Snake Trap
• Wandering Monster - We'll assume he doesn't pick up a high-rolled taunt or divine shield minion from Wandering Monster.
• Explosive Trap

An important note about calculating lethal is that Venomstrike Trap and Snake Trap trigger before the targeted minion is attacked/killed. So if you perhaps planned on removing Misha by attacking it, the 2/3 cobra and then only one 1/1 snake spawns. There were a few lethal paths I thought I had before I realized this.

As far as what actually happened I went with a two-turn lethal by clearing his board the best I could and getting him down to 10 HP and I finished him with Grommash the turn after, and prayed that he couldn't kill me next turn which I was extremely fortunate he was unable to do so. I knew I had lethal in there somewhere but I couldn't math that fast so I came back after the game to analyze this and finally was able to see it. Here's a lethal I was able to come up with, which is actually way simpler than I thought it would be:

1. Play Grommash
2. Bladestorm - Hits 8 minions to bring Frothing Berserker up to 17 attack.
3. Attack face with Vicious Fledgling. Wandering Monster and Explosive Trap activate. Explosive Trap hits 3 minions bringing Frothing Berserker up to 20 attack.
4. Attack face with 4 attack weapon, 11 attack Grommash, and 20 attack Frothing Berserker for 35 damage exactly.

Edit: So I totally thought I could upload a screenshot with text but it didn't work that way apparently, so here's the screenshot of the board state:

https://drive.google.com/file/d/1sKi6SktflSiqfPM6pc2XB9oRji7Kib2G/view?usp=sharing