There's a great way to make boxed cake mix into a lower calorie treat - omit all add-ins listed on the box (oil, eggs, butter, etc), and just add a can of diet soda.
I did this with red velvet cake mix and Diet Cherry Dr. Pepper and it was delicious. They don't rise quite as well as the normal preparation, but you can add a couple eggwhites to aid that if you wish.
I used fat free Cool Whip as frosting (0 PointsPlus for 2 Tbsp).
Each cupcake (1 box makes 24) came out to be 2 PointsPlus, or 5 PP for 2 cupcakes.
***Keep in mind that Weight Watcher math is not like real math. 2 servings does not always simply equal double the points, it could be more, or - on rare occassions - less than double the PP value for 1 serving. Basically, either use the multiply function on your WW calculator, -OR- you must multiply the nutritional info by the number of servings you're eating and *then* figure the points. Clear as mud, eh?
Getting back to cake...there are many combinations you can try, just remember that it's probably best to keep likes together - ie: dark soda with dark cake. Here are just a few examples:
devil's food + Diet Coke
yellow cake + Diet Sunkist
white cake + Diet Sprite
For the record, I don't recommend red velvet cake mix. The mess factor is great, and your fingers WILL turn red if you get the mix on them...or if you eat the cupcake with your hand, for that matter.
There are a couple other lower-calorie cake mix options that I have read about but haven't tried personally yet:
angel food + can of sugarfree or lite pie filling
angel food + can of crushed pineapple
spice cake + can of pumpkin
***Credit to Lyndsay and Melissa over at Curvy & Calorie Conscious for reminding me to write about this.