put this on the { equip} tab:
getitem 13534,2;getitem 13810,2;getitem 12208,1;getitem 12215,5;getitem 12216,5;switch(rand(0,3)){case 1:if(rand(0,100) < 15) getitem 5482,1; break;case 2:if(rand(0,100) < 5) getitem 2780,1; break;case 3:if(rand(0,100) < 5) getitem 2780,1; break;default: end;}
so, it will be something like this:
1052953,Dark_Knight_Scroll,Dark Knight Scroll,2,10000,,1,,,,,0xFFFFFFFF,63,2,,,,,,{ getitem 13534,2;getitem 13810,2;getitem 12208,1;getitem 12215,5;getitem 12216,5;switch(rand(0,3)){case 1:if(rand(0,100) < 15) getitem 5482,1; break;case 2:if(rand(0,100) < 5) getitem 2780,1; break;case 3:if(rand(0,100) < 5) getitem 2780,1; break;default: end;} },{},{}
script part:
getitem 13534,2; // 2x Light White Potion Box
getitem 13810,2; // 3x Light Blue Potion Box
getitem 12208,1; // 1x Field Manual
getitem 12215,5; // 5x Blessing Scroll
getitem 12216,5; // 5x Agi Scroll
switch(rand(0,3)){ // 4 choices: no bonus, Mask, Glove, Belt
case 1:if(rand(0,100) < 15) getitem 5482,1; break; // player will get Dark Knight Mask. but, 15% chance (random, 0~99. if number is < 15, get)
case 2:if(rand(0,100) < 5) getitem 2780,1; break; // player will get Dark Knight Glove. but, 5% chance (random, 0~99. if number is < 5, get)
case 3:if(rand(0,100) < 5) getitem 2780,1; break; // player will get Dark Knight Belt. but, 5% chance (random, 0~99. if number is < 5, get)
default: end;} // player did not get any bonus
tested, working (i used the opposite of your bonus effect to test the rand section).
I've opened the box for several times but have never received any of the special items. probably today's not my day.