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I'm watching the beginning of a playthrough, but it doesn't seem very realistic; it's unlikely to work on the Champion difficulty.
You need to get rid of the golems almost immediately at the start (and almost always the ifrits too), keep the hero moving and don't slow down, and often discard units when gathering resources, divide the djinns, and auto-battle won't work even with wolves. Against skeletons, you also need to discard medusas and take ifrits. You can't lose anyone at the start except for the golems; a little later, the ifrits won't matter as much, but definitely not at the start.
Besides, it's unrealistic to defeat the griffin with a weak hero without significant losses, and after him, there will be level 4 troops and titans. I first went up a bit to level up; by the time the 12 titans arrived, I managed to defeat them without losses by a miracle. The djinns ran out of mana, and one titan was still left, and the dragons had very little health.
I had to go up a bit to level up and then go for the griffins and beyond. One djinn with the "Song" skill is almost always essential, definitely more so than golems.
And the video is 1 hour and 39 minutes long, but I played for several times longer; I only cleared the upper part. I reached the titans around the end of the first month, not on the 4th day at the garrison.