It seems like bleed attack,this code is from it (bleedattack.cs):
m.PlaySound(0x133);
m.FixedParticles(0x377A, 244, 25, 9950, 31, 0, EffectLayer.Waist);
So,i tryed to do it,seems to work,this is my AlterMeleeDamageTo inside my BaseCreature.cs,if you do that all creatures doing melee damage...