"Telekinesis enhancing weapon" how to build?

[PK]

Originally Posted by Lex_BR

This weapon is supposed to be an extremely expensive iridium-lined quarterstaff that can be used as a relay and amplifier for the wielder's Telekinetik powers. In other words, if someone with 10 ST an also 10 levels of telekinesis were to hit you with this staff you would feel the impact of the attacker's regular strenght + 2 or 3 times his telekinetic power.

Sounds like you've got the basic idea down already. Though I might suggest tying it in to the teke's Talent as well. For example, this sounds like a fairly cinematic game, so you might let Talent go up to 6. If you wanted PK Talent 3 to do 2x damage and PK Talent 6 to do 3x damage, you could declare the following:

This weapon increases the effective ST of a telekinetic wielder. Multiply his TK level by [(Talent+3)/3], round up, and add this to his effective ST for all purposes.

It's a teeny bit complex, but you'd do the calculation ahead of time. So a person with PK Talent 1 would add (TK level * 1.33) to his ST, while someone with PK Talent 6 would add (TK level * 3) to his ST. That makes both aspects important.

Just a thought.

I would also like for the more experienced or talented wielders of the Faranian staff to be able to use them in interesting and unexpected ways, such as by hitting the ground bellow them and holding onto the staff as it lifts them up for a super jump, for example.

I'd suggest the rules for Using Abilities at Default (GURPS Powers, p. 173). Since those rules already allow someone with TK to temporarily use it as Super Jump, DR, etc., for a single use, perhaps the weapon could make it easier to do. Maybe high levels of relative skill in the weapon reduce the FP cost and/or penalties. I might do something like:

The staff makes it easier for a telekinetic to improvise with his abilities, as long as he is using the staff as an active part of the stunt; see Using Abilities at Default for full rules. The wielder may use his Will-based weapon skill instead of a Will roll, which allows an experienced user to soak huge penalties; Talent still applies. In addition, reduce the FP cost by 1 for every full 8 character points invested in the skill; at 24 points (e.g., a skill of DX+6) these attempts cost no FP.

Example: Joe has DX 12, Will 14, PK Talent 5 [25], TK 8 [40], and Staff (A) DX+4 [16]-16. When he uses his weapon, he adds [(5+3)/3]*8, or +22, to his effective ST. He is under attack and wants to spin his staff fast enough to provide DR 8 (Directional, Front, -20%; Force-Field, +20%) [40]. This costs 100% of his TK cost, for a -8 penalty, and the two abilities are very different, for another -2. But instead of rolling against Will (14), he rolls against Will-based Staff (18), and adds his Talent (+5), before tackling the -10 penalty. He must roll 13 or less to pull off the stunt. (Without his staff, he'd be rolling 9 or less!) Succeed or fail, the stunt costs him 1 FP -- it'd normally be 3 FP, but his Staff skill eases that burden.

Of course, I'm assuming you'll use Staff skill. It might make more sense to create some new, weird skill for this.

Originally Posted by Jerander

My first thought was Striking ST with Gadget limitations.

I believe the OP is trying to build this as a normal weapon for his campaign, not as a "super gadget" that costs character points.