Summonable Allies with skill-based Frequency?

[Prince Charon]

Basically, instead of the usual Frequency of Appearance, suppose some types of Summoned Allies (especially Minion Allies) appear when you make a skill roll, and fail to appear if you don't. Fluffwise, it makes sense that e.g. if your Force Construct Minion fails to manifest out of your magitech ring when called, it's because you flubbed the Power Ring Operation roll, not because it's busy doing something else. Also, some gaming groups might prefer something more granular than the standard '6-> 9-> 12-> 15-> Always' arrangement.

The question is what problems are there with this, if any, and what's a good way to accomplish it mechanically? I've got two ideas for the latter:

1. Whenever the summoning skill gets closer to the next level than to the previous level, increase the multiplier. So, at skill 8-10, you use the '9 or less, x1' multiplier, at 11-13, you use x2, and so on. Alternatively, switch over whenever it gets above the 'or less' number, so skill 7-9 is x1, 10-12 is x2, et cetra. Not exactly granular, unless you multiply by 1.#, 2.#, and so on, but it fits the RAW. On the other hand, if you only use that skill for summoning, you're effectively just making that skill more expensive.

2. Don't use a multiplier, just add a modifier that says 'Frequency of appearance based on skill, +##%;' but what should that cost?

EDIT: For 2, I suggest that whatever the modifier is, it should be the same regardless of skill level, otherwise you are again making that summoning skill more expensive. Maybe the modifier should be an alteration of the 'Summonable' modifier. So, something like 'Summonable (frequency of appearance based on skill), +##%.'

[Aldric]

FoA rolls are also a daily thing.
So you could start by making it Constant (x4) and then apply both Limited Use 1/day (-40%) and Requires Attribute roll (-10%) or even -5% (a skill roll is even cheaper thant a Per or Will roll)

[Varyon]

Originally Posted by Aldric

FoA rolls are also a daily thing.
So you could start by making it Constant (x4) and then apply both Limited Use 1/day (-40%) and Requires Attribute roll (-10%) or even -5% (a skill roll is even cheaper thant a Per or Will roll)

I always thought FoA rolls were more of a once-per-session thing* - either the Ally is available this session, or he/she isn't (of course, Limited Use isn't really appropriate, as that would let you summon your Ally for 1 minute each day). But Constant + Requires (Attribute) Roll seems the way to go; note changing (Attribute) to (Skill) is generally +0% - I believe this was in GURPS Powers under the "Skills for Everyone" rules. I think that calls for the activating skill to be Hard, but I'd let Average stand in at -1 to skill, or Easy at -2 to skill (Very Hard is normally at +0, but I'd be inclined to make it +1).

That said, Unreliable gives a small discount compared to what we see with FoA (their use of different target numbers obfuscates this a bit, but consider when you compare unmodified (+0%) with Unreliable 5- (-80%), the latter is at 20% cost... but when you compare Always (x4) to Quite Rarely 6- (x0.5), the latter is at 12.5% cost - a greater reduction, for something that happens more frequently). The -10% of Requires (Attribute) Roll is comparable to the -10% of Unreliable 14-. Extrapolating from the existing curve for FoA (which gives an R^2 of 0.9966 using a polynomial or power trendline; I'll use the power trendline here, where (End Cost)=0.0034*(Activation Number)^1.9888), we get an end cost of 65% - so -35%, compared to Always (which is x2.6 compared to the base cost for 9-). That may be more fair.

*Honestly, it should be more of a "Whenever the GM deems it appropriate" kind of thing. If you're about to go out to the dungeon, the GM rolls the FoA of your barbarian Ally to see if he's available to join you. If he is, he joins you... and stays with you until you get back to town, regardless if this happens this session, or 5 sessions from now (he doesn't just up and vanish if he fails his FoA roll on next session, or pop up on his own if he wasn't present but then he made his FoA roll in a later session, because once you set out, there are no more FoA rolls until the GM deems it appropriate for such). Once you're in town, however, Ragnar goes on his merry way, and so the next time you set out, the GM makes a new roll to see if he's available.

[Aldric]

I know the limitations of Limited Use (no pun intended). And I am quite convinced that any ability that is passive or always on, should be treated differently when LU is applied to it compared to those that already have activation time and limited duration, but that's for a different discussion.

I'd use a discount similar to Per and Will for an ability based on a skill, it may start lower, especially for a H or VH skill, but will eventually become cheaper, and I'm pretty sure a character interested in summoning would invest in it.

And yep, FoA for summonable allies is a daily roll, and if they show up, they stay for the rest of the adventure. It was how a low point character I made for a fantasy game was created, stay in town and try to summon your guardian golem each day, if it appeared, hit the dungeon.