Posts: 24
Threads: 4
Joined: May 2019
Like Seravy said, they target resistance. Quick breakdown (apologies if this is stuff you already know, maybe someone else will find it helpful): Each point of Resistance = 10% chance to resist. 4 Res = 40% chance, 6 = 60%, etc. So at 10 resistance, a unit has 100% chance to resist, or is completely immune, right? Yes and no. Most resistance targeting things have a penalty attached. Chaos Spawn's Gaze attacks say, e.g. Death Gaze -4, which means that the target's resistance is lowered by 4 for purposes of the attack, meaning at 10 resistance you'd actually have a 60% chance to resist.
So the obvious solution for gaze attacks is to buff up Resistance to being at least 14 (in the case of the Chaos Spawn). Part of what makes this tricky for Chaos Spawns, though, is their array of attacks - you need Bless to protect against their Death Gaze, but you need Resist Elements to protect against their Stoning Gaze, and I don't know if there's much of anything you can do to protect against their Doom Gaze (but that's also probably not an auto-kill).
So buffing your Resistance high enough can be great if you can hit that magic 14 but it's quite likely that you can't (and even if you can, there's still that Doom damage to worry about). The good news is that Chaos Spawn are relatively slow and, for a Rare summon, not super durable. In other words, take it down from afar. A few Magicians will do much better against one than an entire stack of Wraiths.
Chaos Spawn are a bit like a more extreme version of Night Stalkers, in that way - if you're prepared for them they're pushovers, but if you're not they're incredibly deadly.