So I'm playing Dark Knight now and I'm at level 51. I looked up the 50-60 abilities it gets and was wondering about a couple.

Abyssal Drain. does this just completely replace unleash? It seems beter in everyway except it cost more MP. Like Stone 3 beter than Stone 2.

Sole Survivor. What the hell? Mark a party member and if they just happen to die I get healed? This seems like most useless thing ever. How am I suposed to know if someone is about to die? Is this just one of those PVP things or something?

Thank you.