Crit example

function Item.setRandomCrit(self)
    self:setAbility(ITEM_ABILITY_CRITICALHITCHANCE, math.random(1, 100))
    self:setAbility(ITEM_ABILITY_CRITICALHITAMOUNT, math.random(1, 100))
end

local item = player:getSlotItem(CONST_SLOT_LEFT)
item:setRandomCrit() -- rolls a random crit chance + damage modifier