Many fixes in one mod for Tribes of the East.

Isn't it -1, -1, -10% ?

No. This is talking about an artifact set, specifically its bonus for 2/4 pieces )
-1 -1 -10% = that's the default banshee scream. -2 -2 -20% = that's banshee scream + 2/4 necromancer artifact set. -3 -3 -20% = that's hero Deidra's banshee scream + 2/4 necromancer artifact set ))