Bonestorm
15 Runic Power per sec, Instant, 1 min cooldown
A whirl of bone and gore batters nearby enemies 3 times per second to deal minor Shadow damage, healing you for 1% of your maximum health per strike.
So it's going to hit each target 3 times per second and heal 1% per hit. So if it hits one target that's 3% heal per second.
Does that mean if it hits 3 targets it's going to heal you for 9% per second? I don't see a minimum amount of targets that can be hit by it, so if you're tanking 6 mobs and it hits all 6, does that mean you're going to be healed for 6 * 3 = 18% of your HP per second?