A lot of the Outsider's behavior makes a lot more sense in light of his And I Must Scream situation. He always claimed he was bored, which initially just seemed like the feelings of an arrogant god, but if he's stuck in a perpetually dying state and unable to interact with the world of course he'd be bored. Giving people the mark was probably the only way keeping him from going completely insane, which is also probably why he hates it when people act predictably.
The Outsider giving people the mark might have also been his way of trying to find someone to free him. He couldn't say what he wanted directly because they might stop him, but if he caused enough chaos he would eventually cause Billie Lurk's two dimension problem.
His offers of power can be seen as him doing to others what the cult did to him, thrusting huge supernatural power on someone who suffered misfortune. The fact he usually chooses to mark people with humble beginnings like Corvo, Daud and Delilah may also be because they remind him of himself.
A teenaged old boy with odd abilities and knowledge dumped into an unfamiliar time in a foreign country has a very short life expectancy, particular in a setting modelled on industrialised England. Daud would be glad — his vengeance is complete either now or very soon.
