the game max level is only til lv27 ....tbh, is abit hard to play nightmare+all trials with mage due to skill cool-down time too long ,on the other hand , assassin rogue are just same whether u play on easy or nightmare ,cos even in nightmare u still 1-2hit kill everything especially with hidden blade new upgrade (no witness) which can proc hidden blades on every nearby enemies 3hits , just go stealth and use hidden blade to land every hit critical,even if the enemy doesn't die , they are near death , just useflank attack to go back stealth and use throwing blades to kill the remaining ....
hahaha seriously? try this fight on nm with all trials on with an assassin, I just tried it with cole as an alternative to my usual mage quisi with some super daggers 162 base main hand, 191! base off hand damage equipped and (I had 32% attack, 203% crit damage bonus, 175% flanking damage bonus, masterworks: chance apply walking bomb, hidden blade x5, target explodes on kill for 75% damage, also 80%/ maxed out frost resistance and mighty offense tonic)...well I managed to take out 1 of the 4 despair demons so far before they scatter in all directions (and generate barrier!) and even with the frost resistances damage me so fast I do not have time to restealth. and stuff like twin fangs from behind BARELY scratched it with the stats above! The only way is to stealth, mark of death, hidden blades followed by deathblows, and that takes out half the health of one demon if you are lucky before it barriers itself and jumps away. And the barrier soaks much more damage than the actual health bar on them. It's the "secret boss" of the hakkon dlc.