[d20 Modern] AdC design: spell as class ability

[The Shaman]

In selecting a spell as an extraordinary or supernatural class ability for a Modern advanced class, is the general rule to make the class ability available at a level commensurate with the level of a caster of the same spell?

For example, if an AdC had gaseous form as a class ability, would fifth level be appropriate placement?

If a spell is available as a class ability, are times per day limits equal to the number of time the spell could normally be prepared in a day by an arcane or divine spellcaster reasonable? Using the example of gaseous form again, would it be reasonable to introduce it as a 5th-level class ability at 1/day, then make it available 2/day at 7th level?

Is this approach over- or underpowered?

 

[tjoneslo]

For a D&D class I'd call this a touch underpowered. The idea being that the class feature should be able to do things that no one else can. I'd introduce the power a level early (say 4th), then increase more slowly, say 1/3 levels.

For D20 modern, it may depend upon how much arcane firepower you expect. If there are many mages (in theory), I use the above. If there are few, or hidden, I'd use your approach.