This one may be the one that makes me not want to play any more. 4 Arcane Imps and 2 Frost Imps, a room with walls, broken terrain, and low walls that block movement but not ranged attacks. Frost Imps chain casting freeze spells that keep you from moving into melee range, they all have range 6 or range 8 magical attacks that can shoot across the map, and multiple runs, so even if you manage to evade or kill the frost imps and prevent the freeze spells, you can't keep close enough to kill anything without them dancing away. And if you manage to kill a couple and take up a defensive position, the AI will cheerfully do nothing -- not even move -- for 20 turns (I counted) waiting you out. Can't get in range to hit them with discard attacks, the mage can't go toe-to-toe, and the fighter gets chewed to bits moving one square per turn.
Ultra long range wizard. Step warrior. Lifesteal Priest. Bring some Purge. Hide behind corners and wait for them to get in step range with your melee types. Resistant Hide on your Wizard, Shimmering Armor on the others. Missile Deflection in shield slots. Wizard should make the frost imps priority in case you lose the wizard early from focused fire.
After you take a few of them out sitting back and healing up will help a lot as they tend to do nothing then as you pointed out. Also if you still have issues with this stage after using what xienwolf said you could always level another wizard to help as they have the easiest time with these nasty buggers.
I did what xienwolf suggests, but all dwarf (which is even worse becuse of 2 movement only!) with a lot of armour, the fire/cold encumber spells do very low dmg, so even when trapped in one spot they aren't doing any/much damage
In addition to what xienwolf said, also check if you can get boots with Sprint or Wild Run. And lava is once again a good solution. Also in case it helps, here's that particular fight from my beta diary: https://forums.cardhunter.com/threads/zalminens-beta-diary.608/page-7#post-11596 (slighly outdated as some minor stuff has changed since then)
