Bat constellation is a mess to be honest. While the proc is actually quite good and may rival Falconswoop in terms of single target (but only if you focus on pierce and vitality), other nodes just don’t stitch together. My analysis and suggestions come from the assumption that the devotion will be mostly used with Phantasmal Blades.
First node:
+15% Vitality Damage
+15% Bleeding Damage
Third node:
+24% Vitality Damage
+30% Bleeding Damage
The main problem here is that Bat doesn’t give pierce damage, at all. Even if the proc uses it. Best attack devotions actually give the %bonuses to the damage types that proc uses, so it’s safe to assume that the lack if +%pierce damage hinders the potential of this constellation. So my suggestion is to switch %bleed to pierce.
Also, bleed/vitality doesn’t conceptually fit the Bat, because this damage combo is Devouring Swarm and Bloody Pox. Would’ve made sense to have something like that on Rat instead. Pierce/Vitality fits better because it’s for Nightblade.
Next, second node:
15% chance to do ~120 Vitality Decay over 2 seconds
Vitality Decay, really? Come on, +%vitality decay is absent in masteries and is very rare on gear besides a few faction greens and high-end legendaries. Why it’s on an early devotion like Bat? Not to mention that Bat itself doesn’t provide with +%vitality decay. And even if we close eyes on this, a simple flat DoT damage node is just weak. I don’t suggest adding +%vitality decay to it, like it’s done with Rat, Manticore, Fox, Bull. I suggest flat vitality decay to be removed from bat.
Fourth node:
+30% Life Leech damage
3% attack damage converted to health
There again, a node that doesn’t fit well. I understand that it’s a Bat, but Life Leech Damage is even more garbage than Vitality Decay imo. It’s so irrelevant that it doesn’t even appear in character stats. Moreover, Bat doesn’t even provide with flat Life Leech damage. Personally I don’t see the reason why there has to be three devotions utilizing such an irrelevant stat (the other two are Ghoul and Vulture); coincidently, all three are mostly avoided by players, except for maybe Ghoul for it’s proc.
So how would a perfect Bat constellation look to me?
First node:
+15% Pierce Damage
+15% Vitality Damage
Second node:
Increases Armor Piercing by 50%
Third node:
+24% Pierce Damage
+24% Vitality Damage
Fourth node:
+40% Bleeding Damage
3% Attack Damage Converted to Health.
Proc:
70% chance to pass through enemies -> 100%.