Trying to succeed in the App Store is a whole different world in itself.

In general advertising is tough for any $1.99 product. For this particular product I'd say it's even tougher. A dice roller is simply not a mass market product. So most of your advertising dollars are going to be wasted on people who don't care.

Asking sites for reviews and maybe even finding some D&D-type sites that would be willing to look at it and review it would be your best bet -- and just takes your time.

An ad-supported version may help visibility, but don't rely on iAds alone. The fill rates are not high enough. Alternatively, if there's a simple way to make a Lite version without giving away the whole thing, that can also be a way to get increased visibility.