Black Book

For me this was the only method that works to win the fight

All credit to Issac Strom on YouTube

Here's how to defeat Prokopy in 3 rounds by stacking Waste damage on him

Round 1: Headless (self), Dead Man (enemy), Blood-Burn (self), Firm Knife (self)
Round 2: Headless, Red Sun (both on self)
Round 3: Breakbone, Breakbone, Herod Bones (all on enemy)

At the very start of chapter 3, you will head back to your beloved's grave to pay respects after going through a few small map nodes. When you return to grandpa's hut, talk to the visitors and a priest will come asking to investigate a cow that was cursed in his chapel. Agree to help.

As you make your way through the map nodes towards the chapel, when you arrive you can grab some herbs nearby. Head inside the chapel, examine the interaction points before talking with grandpa and then he will send you to look for clues. Examine the chicken tracks next to you and then outside, examine the cloth hanging on the tombstone. Talk with grandpa again and he will make the tracks glow.

Head outside and move upwards to a new area, enter the coffin and after speaking with grandpa's long dead teacher, a fight will ensue. Use cards in this order:

Turn 1: Headless, Ognevitsa, Blood Burn
Turn 2: Headless, Dead Man, Firm Knife, for grandpa's skill
Turn 3: Breakbone, Headless, Herod's Bones
Turn 4: to end turn.

Once he dies, this achievement will unlock.