Magnus is the 4th playable character to join your team and this is one of two moves he has that are connected to achievements. Chain lightning is an awesome attack for many reasons. It is silent, it ignores armor, it can be chained (duh) and you do double damage to a robot. A normal chain lightning will do 4 damage but against a robot it will do 8. This comes in handy especially in Metal fields
. If you haven't gotten it in metal fields then make sure you finish off MIMIR Z600 with it when you face him and also make sure you EMP grenade him to start for a much easier time.
His other move is Puppeteer. When you get to the zone Izza and Fala
there is an enemy on the roof that approaches the ladder after he is done having a conversation. He has 100% chance of success due to his tiny brain. Use Magnus on the first turn of the ambush, Puppeteer him, pause and quit. Do not do this on the last turn or the game will save and this won't work. Repeat until you have 10 and you will have this annoying achievement out of the way too.