How to get the Conscientious Objector achievement SOLO

For the method, you must play as the red knight, as he does damage with his magic jump. The game oddly does not give you XP for dealing damage with a magic jump despite it dealing damage, and the game counts getting XP as attacking something. Make sure you have unlocked the magic jump and put all of your skill points towards magic if you haven't already.

I would recommend using the Beholder pet (gives 4+ magic extra damage) and a weapon that gives a magic damage bonus as well. You should be one shotting all of the barbarians if you have a high enough magic level.

For the 2 bosses, they don't take damage from magic jumps. HOWEVER, you CAN damage them with your magic lightning attack because it doesn't count as damage in logic for the achievement, just make sure there are no barbarians in the way (get rid of them by using the magic jump) otherwise you might accidentally hit one with the lightning and you'd have to start all over again.

Some other advice is when you beat the Castle Keep level and move onto the Barbarian War level, do not try to go to any other level in the game on the map as it will erase the progress on getting the achievement. Do not attack enemies by mistake either, i would recommend temporarily binding it to another key on your keyboard that you for sure won't accidentally click.

So yeah, that's the method, hopefully you got the achievement.