FASA Games, Inc.

How are spells that allow additional targets on extra successes (like Air Mattress or Lightning Bolt) handled if potential targets have different MD?

From reading the text, it seems like the standard way is that the spellcasting test is rolled only once, and the initial primary target's MD is used to determine number of extra successes. Then the initial roll is compared to the additional targets, and if the unmodified roll hits thier MD, the additional target is hit as well.

The problem in my mind is what if the potential targets have wildly differing MD?
Lets take an extreme situation where you happen to be fighting two Espagra (MD 15). Lets say that there also happens to be a Bear in the area (MD 5) or you might well have brought a Lizard (MD 6) along for this very purpose.

You decide to cast Lightning Bolt, but know that if you target an Espagra, you will need to roll a 20 to get an extra success and also hit the 2nd Espagra. The interesting thing is that if you target your lizard, if you roll at least a 16 you will have two extra successes (against the lizards MD of 6) to target two additional creatures. You could thus hit both Espagra (and your poor unfortunate lizard) with a roll that is lower than the 20 required if you target an Espagra directly.

It seems like the best way to handle this is to compare each additional targets MD against the roll result with a -5 per previous target. So if all your targets have about the same MD, things behave as they currently do. But if potential targets have wildly differing MDs, you don't get bonuses for targeting the lowest while also hitting the highest.

I suppose this is really just a solution in search of a problem, but I've known players who would try this.

It isn't in the rules, but I'm going to make it official: you can't bounce extra successes to higher MD targets in that way. You want to hit the lightning lizard? You need to target the lightning lizard. No bootstrapping.

generally isn't it the rule for about anything when you use something that hits multiple things you use the target with the highest defense as your target number. After that result have at them all

But that just brings us back to the origional question.
If you target a common iguana (MD 6), then if you happen to hit that lizard with a 16, you have generated two extra successes, which could be used to hit two Espagra (MD 15). Where if you just target an Espagra, you need a 20 to generate the extra success to target the 2nd one.

Magic works mysterious ways

Chris, use bolt at poor lizzard, hes so weak (MD) that lightning will go get some more targets, in your example espagras ( if initial roll is at least their MD).

It almost seems to be on purpose, with a theme of "path of least resistance". Compared to Fireball - it makes the caster take different tactics.