Frostfire Finesse

Step 1: Get the fire charge from the red crystal then drop Myrrit on the pressure plate under the other (blue) crystal. Now you can walk over to the frost key and pick it up. Stuns do not keep you from finishing either step. Go back to Myrrit

Step 2: Get the frost charge from the blue crystal then drop Myrrit on the pressure plate under the red crystal. Now you can walk over to the fire key and pick it up.

(These steps can be done in either order)

Step 3: Use the action button to combine the keys. Go to the chest and open it.

1. No digging - just walking with Myrrit around
2. Put Myrrit on the pressure plate under one of the crystals (Key number 4 in the interface)
3. Click the other crystall to get the opposite buff
4. Go to the other side of the room and get the glittering key (you need frost buff for fire and fire buff for frost)
5. Take Myrrit (click him) and put him on the other plate (key 4)
6. Get the other buff by clicking the other crystal
7. Get the next key
8. Click extra button to create key
9. Open chest
10. Be happy :-)

When doing this puzzle, I missed the fact that the pressure plates and the gems above them were separate entities. The push plates are for Myrrit , and the gems are clickable for you.
All you need to do is click the gem Myrrit isn't under to get the buff, collect the key, then swap plates/gems. Rinse and repeat.