I did some more testing and i found out there must be something wrong with this code:
rmAddTriggerEffect("Unit Create");
rmSetTriggerEffectParamInt("PlayerID", 0);
rmSetTriggerEffectParam("ProtoName", "Serpent");
rmSetTriggerEffectParam("Location", "" + (rmXFractionToMeters(rmPlayerLocXFraction(i)) + 25) + ",0," + (rmZFractionToMeters(rmPlayerLocZFraction(i)) - 25));
it worked fine in single player, but the effect doesnt work in multiplayer for some reason