You need more then one sword. The one that causes the enemy to bleed/poison stacks up so just keep hitting the scare crow dies.
finally defeated the scarecrow. "Equipment", namely with the help of purple poison knives, 3-4 pieces seem to be enough. We stand under the scarecrow so that the knives touch the scarecrow and poison it. Then you need to eat a piece of the philosopher's stone so that the hero says a line, but do not cancel the line to stop time... We wait 30 minutes, achieve 240k damage, the hero says a line, the scarecrow finally dies.
To stop time, you can break a weapon and not activate a new one, but in this case you will have to wait for the required damage for several hours.
The more damage the weapon has, the more damage from the poison will be added per "1 stack"
By the way, if you quickly run outside the map and return, you can have time to kill several scarecrows.