Build Question - Compound/Conditional Power

[Psillias]

So...I'm still trying to convert all of the Gamma World 4e creatures into Hero.  I'm currently stuck on a power that seems like a compound power...but has a weird conditional requirement:

 

"The porcupine plant attacks by firing 1 quill per available segment.  Each quill causes 2d6 RKA and is coated with a destructive poison.  A hit of 4 or above on the required to hit roll harpoons the target, lodging a barbed quill in the victim.  The horl choo then retrieves its prey with a tough, thin vine which is attached to the base of the quill, dragging the character to itself with an effective strength of 15.  Strong characters can resist the horl choo's pull and characters not entangled can try to sever the vine."

 

I can make the compound power of the barb + the vine...but how do I add the condition of needing 4 or above on the required to hit roll?

 

Thanks for any assistance anyone can provide!

[sentry0]

Maybe an Activation roll at 17-.  It should equal the same chance of failure at 0.46%.

[Psillias]

So a limitation of an activation roll for the second half of the compound power then?

[sentry0]

Just now, Psillias said:

So a limitation of an activation roll for the second half of the compound power then?

 

I think so.

 

What was the original chance of it activating?  Like was it a 5 or greater on a d20 roll?

[Psillias]

4 or greater over THAC0...

[Gnome BODY (important!)]

Why not just Limited Power: Power only activates if to-hit roll succeeds by margin of NUMBER (-something depending on how big NUMBER is)?

[Psillias]

Thanks Gnome.  So make two separate powers?  The RKA and then the Limited Power with the vine if it activates?

[Psillias]

That appears to have done the trick.  Compound power with the second half being a limited power. 

 

Thanks Gnome and sentry0!

[Rails]

I'm not at home to be able to check my books, but I seem to remember some venoms in the Bestiary being written up as linked powers (Drains, I think, linked to HKAs) with "Only if HKA does body damage (-1/2)".  It seems like that approach would also work here.  The value of the limitation could change depending on how common resistant defenses are in the campaign, of course.

[dsatow]

Another way to do this is to make the poison an NND and add another defense in that the killing attack needs to do 1 Body to the target in addition to the defenses like LS:Poison immunity.