Hit a rock with Mjolnir and send it back where it came from.
Hit five enemies with a single bolt of lightning
Get 3 stars on level 1
Get 3 stars on level 2
Get 3 stars on level 3
Get 3 stars on level 4
I got 3 stars on Ragnarök, and all I got was this achievement
Defeat 1000 enemies with lightning strikes
Defeat 5000 giants in total