try this
prontera,155,181,5 script Sample 757,{
set .RequiredID,20078;
if( !countitem( .RequiredID ) ){
mes "You need 1 "+getitemname( .RequiredID )+" to exchange.";
}else if( rand(100) < 20 ){
mes "You have failed in this trade, "+getitemname( .RequiredID )+" will be removed.";
delitem .RequiredID,1;
specialeffect 155;
}else{
mes "Congratz.....";
specialeffect 154;
set .Random,rand(100);
if( .Random <= 5 ) getitem 5738,1;
else if( .Random > 5 && .Random <= 10 ) getitem 5443,1;
else if( .Random > 10 && .Random <= 14 ) getitem 2294,1;
else if( .Random > 14 && .Random <= 17 ) getitem 5509,1;
else if( .Random > 17 && .Random <= 19 ) getitem 5150,1;
else if( .Random > 19 && .Random <= 20 ) getitem 5426,1;
else
mes "You gained nothing.";
}
close;
}