Completing the quest the way Raphael asks is good for your relationship with Astarian and Shadowheart but involves one of the hardest fights of act 2.
The difficulty of the fight is a bit subjective imo. It shouldn't be a deterrent for trying it if you are interested on doing Astarion's quest.
Without spoiling too much: there's this npc that Raphael asks you to kill inside the Temple of Shar, there's also a quest and a minor fight that is tied to it and involves talking to some rats. Be careful of
not doing the rat thing before talking to the npc because it may cut you out of Astarion's quest due to a chain of events.
Also there's a way to solve this npc thing with dialogue and keep Astarion's quest if you pass an insight check.
