Swallow Soul is a 10s heal over time that keys from the damage you did, the last time you used it. I'm gonna say it ticks every 2s, since that's what skills normally do. The heal ticks cannot crit, but can be keyed from a critical hit, making them stronger in that case. For example, you could force a critical hit via cloaking and using Swallow Soul once, when coming out of cloak.

Damage done is also impacted by the resistances of the monster or player and by Battle Spirit. The most interesting case is Imperial City. The heals from damage against players will be low, because of Battle Spirit and because players tend to have high resistances or other defensive measures, such as Major / Minor Protection and stuff like DK Corrosive Armor. PvE mobs in IC, however, take your full damage. Thus you can key a Swallow Soul heal from an IC mob for much better healing. This isn't very practical when that skill is also your spammable, but it's worth mentioning in case you (are forced to) play defensively.

Then there's the Soulcleaver set from Infinite Archive. This has a double effect on your Siphoning from damage heals. It buffs the damage of Swallow Soul in the first place and, thus, indirectly the healing. The resulting heal is, then, buffed a second time by the set. I believe this is deliberate. It's less than it seems, because you're buffing a fraction of a fraction, but it does up Swallow Soul healing to something like 44%, last I looked. Could even be a bit more in the current patch.

Arboz wrote: »

Yes, in the meanwhile I moved away from such skills in PvP and focus on a pure glass cannon style. Nightblade survives better with hit-and-run than with heals, my experience so far.

Yeah, while we don't have subclassing yet, you might as well lean into nightblade's unique playstyle on that class. That said, I use the Siphoning heals and play a sustain build. You can make it work:

https://www.youtube.com/watch?v=7IdxmUID8OQ