Some of the shaman supps to which (first circle) hell mobs are immune don't have echos. Most of them (blind, weaken, etc.) say something about how you're not powerful enough to blind/weaken/etc. the mob, but damnation (and I think wither) give no echo at all. The mob isn't affected, there's no "failure" message, just...nothing. I didn't try all of them, so it may also apply to some others in addition to damnation/wither.

n/t