The mechanic
The Harvest King is a slow, armored scarecrow lord with the largest health pool of the early roster. He plods up the path and does heavy base damage, but the real pressure comes from what erupts out of him.
At 80, 60, 40, and 20 percent health a murder of 4 crows bursts out, 16 crows across the fight. The crows are fast and unarmored, and they flinch hard at crowd control the same way goblins do, so slows and stuns grip them longer than normal.
When the king finally collapses he leaves behind 2 thresher husks, slow heavy-hitters that trail in after the crows as the last thing you have to clear.
How teams beat it
Lean on slows and stuns for the crow bursts, since they are extra vulnerable to crowd control and will otherwise race past your towers. Save single-target damage for the two slow thresher husks that follow the king's death.
Like every boss, it fights inside the showdown rules: kill it and it respawns about twenty percent stronger on the rival's lane, let it leak and it crosses unescalated. The full showdown rules are in How a match works.
