Actually, is easier than it looks like.
Close Call Achievement Guide
- Win an encounter with 1 unit left with 1 HP left.
Start a run in the second campaign (Orcs Dominion) with Asra and your weakest allies – Arcane Wizard and Sorceress fit well here. Search for a first battle, and decimate all enemies except one; let that one kill your allies just by passing turns over and over,
Lastly, let it defeat Asra – since she’s going to trigger “Shield of Shadows” will survive with 1 HP garanteed. Finish off that enemy.
And there you’ll have both Close Call achievement and Witch Doctor.