on src/map/status.c find this line:
case SC__UNLUCKY:
{
short rand_eff;
switch(rand() % 3) {
case 1: rand_eff = SC_BLIND; break;
case 2: rand_eff = SC_SILENCE; break;
default: rand_eff = SC_POISON; break;
}
change to this :
case SC__UNLUCKY:
{
short rand_eff;
switch(rand() % 3) {
default: rand_eff = SC_STUN; break;
}
and then recompile your server.