Alternativee Abilities versus Alternate Form

[GreatWyrmGold]

Characters with things that can be other things instead or are otherwise mutually exclusive are common in fiction, even without getting into the super-, sub-, and sister-tropes of the two I've shamelessly linked. In GURPS, there are three methods I am aware of of creating such mutually exclusive sets of abilities:

1. Alternate Form (15 points plus "base form" plus 90% of the difference between base and non-base "forms"). Requires concentrating for ten seconds (can be modified, of course), and can be forced into "base form" at any time by disabling the ability.
1b. AF with Once On Stays On (22 points plus cost of most expensive "form"). Requires concentration but not subject to being forced into any one form (though disabling prevents changing).
2. Alternativee Abilities (most expensive ability plus 20% of cheaper abilities). Technically, all the abilities are one ability, making it relatively easy to cripple them all at once. Also, there doesn't seem to be any required activation time.
3. Split Personality (-15*). Technically only allows mental disadvantages and quirks, but I see no reason not to allow mental advantages into the mix—or even to build involuntary shapeshifting disadvantages off of it!

#3 is different enough from the others that its purpose is obvious; my question today is what hidden advantages the Alternate Form of approximating these variable abilities has over the Alternative Abilities.

[dataweaver]

I'm going to address the “Once On, Stays On” version of Alternate Forms with respect to Alternate Abilities, since the benefits of the default AF over OOSO AF should be obvious.

Alternate Forms vs. Alternate Abilities: you only pay for your forms once. Consider what happens if you have three 100-point forms: you pay 100 points for your most expensive form, plus 15 points for each of the others. If you were to purchase them as Alternate Abilities, you'd need to pay 100 points for the first form and 20 points for each of the others.

The Alternate Forms pricing scheme is consistent whether you’re talking about three 100-point forms, three 0-point forms, or three -100-point forms, since all you're paying for it the most expensive form and the number of alternatives. In particular, note that there's no assumption in the Alternate Forms pricing scheme that any of the forms have positive point totals: if you're in a low-fantasy setting where all of the races are zero-point templates, a shapeshifter who can switch between two of those races is covered. Likewise with the absurd extreme of the “weresnail”: since Alternate Form assumes that switching forms is always voluntary, the cost is always positive.

By contrast, pricing it like Alternate Abilities would get you into trouble if: (a) there was a lot of overlap between the forms (e.g., two 100-point forms with only ten points spent differently between them) or (b) the forms have very low costs (e.g., zero or negative costs).

All that said, I'm not particularly happy with the results. The default length of time needed to switch forms strikes me as excessive, and 15 points for an Alternate Form strikes me as too much. In my games, switching forms takes a concentrate maneuver by default; and the cost is full price for the most expensive form, plus 1–10 points for each Alternate Form: 10 points if the alternate form is up to 10 points cheaper than the base form, minus one point for every additional ten points cheaper the alternate form gets, to a minimum of one point per alternate form. Modifiers that would affect one's ability to shift into the form get applied to that 1–10-point “control cost”; usually, we're talking Limitations.