It's synchronized so no it should not cause a desync.
^Are there unsynchronized variants?
It doesn't depend on where it's used? Like this desyncs?it would crash if you used it for anything in multiplayer
local string s = ""
if GetMouseXLocal() > 0 then
set s = "MyEffect.mdl"
endif
call AddSpecialEffect(s, 0, 0)
^Are there unsynchronized variants?
Yes and in WC3 you would've DC'd.It would have weird gameplay issues tho (like in PoE) where if the ping is off, you're killing the boss while everyone thinks you're in the room behind