Come to think of it, this skill is not as powerful as it seems.
Yes, you get 280% damage for 3ap(chameleon cloak+mortal blow), the special effect [hit enemy(vitality >20%) with this skill and its vitality drops below 20%, the target instantly dies] ignores armor,but it cost 3sp and can only be used once per combat.
For those who don't use scrolls, to max out one turn damage, skin craft(combine with adrenaline&flesh sacrifice) is essential, so if you want to use mortal blow,you will also need apotheosis, which means you get 280% damage for 5ap(apotheosis+chameleon cloak+mortal, a little more than 280% actually as apotheosis give 5 finess),only 30% more damage than two and a half basic attack.
For a 4ap rogue one turn maximum damage(skip the next turn as a result),backlash(85%)+overpower(150%)+adrenaline+flesh sacrifice+crippling blow(115%)+skin craft+adrenaline+flesh sacrifice+overpower+crippling blow deals 615% in total.
Meanwhile Apotheosis+adrenaline+flesh sacrifice+backlash+overpower+skin craft+adrenaline+flesh sacrifice+backlash+chameleon cloak+mortal blow only deals 600% in total.
Yes,like other scoundrel skills, mortal blow can backstab.
BUT in the late game, the base damage of a dagger is about 55% that of Two-Handed(82.5% when duel-wielding. One-handed weapon is about 64%, 96% when duel wielding. Staff, crossbow are only a little less than two-handed, almost the same), meanwhile other class can reach 90% critical chance. For a 22 level character,20% from weapon,15 from 15 attributes in wits(LV22, 45 attributes in total,30 to finess), 10% from hot head,12% from peace of mind, 14% from eternal artifact enchanted necklace with giant flame rune,5% from wits in rings each(10%),5% from wits in trousers, 4% from belts, that's 90% in tota (Although in order to get all these equipment, you need to check out merchants many times).
Look back at scoundrel skills, only 3 vitality-damaging skills' damage/ap ratio is more than 50%/ap(basic attack), while two of them cost 2 or more source. 4 equal to that ratio. 3 less than that. None has hard control effect like knocked down(terrified may count but it's resisted by magic armor and Terrifing Cruelty has the WORSTt damage/ap ratio while costing 3ap).Don't forget dagger has the shortes range and all scoundrel AOE skill damage is a joke compared to magic. They really should think about buffing scoundrel skills.
Return to Mortal Blow. It needs a CD, Less SP COST(Considering dagger's damage, maybe 1sp lIke overpower). (NO ADDING AP COST ******* thank you.)