Jagged Alliance: Rage!

Minimum 2x playthroughs for this. 3 if you want to get the achievement for 2 mercs only

I did:

Easy Playthough - Raven & Shadow - finished game with no extra mercs
Normal playthrough - Dr Q and Vicki - then added Grunty (Coz I didn't know where to find Fidel)
Hard - Shadow & Ivan - later adding Vicki and Fidel.

This final playthrough popped:
Use all rage powers (as you need Fidel too)
Finish with all mercs
Finish on hard

I would not recommend using Ivan on hard - he is a bit of a hard target to hide. Shadow and Raven would be optimal I reckon.