[Anaraxes]

The point of that last sentence is just to say that GMs can, if they wish, waive the requirement to buy Affects Substantial if you have mental abilities that can't (for whatever reason) affect the material world.

See earlier in the box. AS (B63) is required on the Insubstantiality ability itself if an insubstantial being can affect the material world in some manner. That's either mental abilities, or physical abilities with AS (B102) on that individual ability (say, an attack). If you can affect the material world while insubstantial in any way, you have to buy AS (B63) on your Insubstantiality. Two separate considerations: does Insubstantiality need AS (B63), and does the attack ability need AS (B102)? Four possible combinations.

That AS on Insub cost is independent of the cost of buying an ability that's good at affecting the material world. Physical abilities will _also_ need AS if they're to affect the material world; mental abilities _may_ have AS if you want to buy off the default -3 penalty for using them cross-plane, but they affect the material by default.

It's possible to have a concept where the character can't affect the material world at all while insubstantial, because they lack any such abilities. The baseline assumption for Insubstantiality is a middle case -- mental abilities / spells / psi can affect material targets at a penalty, physical ones can't at all. But if your concept calls for being completely unable to affect the material world while insubstantial -- even though you have a mental ability that normally could -- the GM can allow you to skip that requirement that you add AS to your Insub just because you have that mental ability.

To make it more concrete, assume a horrible Danger Room training accident puts Jean Grey's mind in Kitty Pryde's body. So she can turn insubstantial, because Shadowcat. She's also a telepath, because Jean. But, for *insert reason*, she can't use her telepathy while phased. So, no need for Jean to drop a lot of CP upgrading all her psi abilities. The concept calls for an exception to the default rule that Insub lets you use psi at -3 but requires AS on Insub. But here, we skip the AS on Insub at the cost of not being able to use psi while phased. Kittyjean could use psi normally when she's not phased, though.

Your default phasing telepath would normally be able to use their psi at -3, and so has to buy AS on their Insub ability. The centuries-old ghost with lots of practice at contacting mediums can use their otherwise identical TP at no penalty, so they buy AS on it, _and_ on their Insub. Their poltergeist buddy has TK which can throw things around in the material world even while he's completely undetectable, so he has to buy TK with AS, _and_ add AS to his Insub. The newbie ghost from the PC that just died has no TP or TK, can't contact the material world at all, and so doesn't need to add AS to his Insub, at least until they acquire some cross-plane ability.