So I have finally gotten my little hands on a Promissory Note. I went and did some testing and oh boy it's not that great.

What is does
The Promissory Note gives you Normal Defense Increased as well as more normal defense as your health gets lower. After some testing, I've found that note does not perform better than Penta-Heart Pendant in most situations due to a mechanic in which you are left alive by a hit that would have killed you, this mechanic makes Promissory Note almost useless. That's the bad news. The good news is that the note is pretty good in Unknown Passage as well as Tier 2 and Tier 1 Stratums, outperforming Penta in some cases, however it still sucks for the most part in Tier 3. I have a few ideas to make this trinket a bit better.

Rework Ideas
Idea 1: Same Mechanic Different Execution
How about instead of giving us increased normal defense. The Promissory Note just gives us a Defense Orb Buff at different levels of health. Defense Orbs buff all the defenses that we currently have, so it'll make the purpose of the Promissory Note much better.
<100% - 1 Defense Orb
<50% - 2 Defense Orbs
<30% - 3 Defense Orbs

Idea 2: Different Stat
How about instead of increasing normal defense. We increase a completely different stat? I think if we go this route, Misplaced Promissory Note should give increased damage with less health, becoming a risk-reward type trinket. This effect will not stack with multiple Misplaced Promissory Notes.

The effect will start at <60% health, giving you a buff of +5% damage.
I think that at around <10% health you'll reach the maximum buff of +30% damage.

Idea 3: Entirely New Mechanic
How about instead of increasing normal defense, Misplaced Promissory Note will give you temporary invincibility upon reaching the threshold? This'll only proc once per life, so you can't abuse it. Upon reaching <10% health you'll be granted 3 seconds of invincibility. This effect will not stack with multiple Misplaced Promissory Notes.