In all fairness, you should announce the effect you're going to add in prior to the roll.  ::)<br/><br/>Otherwise in any high roll, you're going to have players go 'oh, seeing as I hit them by that much, I'm going to add this effect in now, and this one and... that one also...', which goes against the rulings of some effects (like homing for example).<br/><br/>Throwing in an extra effect as a gamble pre-roll is fun as fuck though.