item of power - sword of Heimdallr

[Kiero]

2. Killer Blow is really weak, possibly as a way to balance out its stackability. Balancing against it seems slightly unwise to me.

Killer Blow is one of those Stunts that seems to recur in every FATE incarnation, and it's worse than weak, it's worthless. For a Fate Point you could get a regular +2 to hit (which is also effectively +2 damage since shifts=Stress) via Invoke, which didn't cost you a Stunt.

So for the cost of a Stunt, you can spend an FP and get a net benefit of +1 Stress, without any bonus to hit. That's just rubbish.

[Silverblaze]

Whilst it is rubbish, you can add that on top of the attack to get three more damage beyond tagging aspects etc for three more damage.  I wouldn't call it useless, just not very useful.

[Becq]

2. Killer Blow is really weak, possibly as a way to balance out its stackability. Balancing against it seems slightly unwise to me.

No argument from me; in fact I already pre-agreed with you on that point. 

3. Would limit the final version of Blessing Of Heimdallr to one use per action. Otherwise I like it. The part about locking down a die that rolled +1 is clever, I will steal that idea.

It's inherently limited to one use per attack because no aspect can be invoked twice on a single roll, including "the aspect linked to the Sword of Heimdallr".  I suppose someone could try taking multiple aspects all referring to the sword, but my intention was that only the aspect that was specifically linked to the IoP (per the IoP 'Musts') counts.  That said, I think you could potentially invoke it (and get the bonus) multiple times as part of a sweep attack (once against each target) and this is probably fair.

And I can't claim credit for the cleverness of the mechanic; I stole it from the 'Unshakeable' stunt from YS.  But I agree; I like it too.

[Sanctaphrax]

Ah, very clever. I totally forgot about the one invocation per aspect rule.

Using an Unshakeable variant on your own rolls never occurred to me.

Actually, my seeing that is responsible for the Probability Manipulation power that I wrote recently.