There is no card page for Parallel Agnes, so let me leave this here for you all instead. For anyone wondering what that even is, its some fantastic free content from a recent FFG article (Link here)

.

Hello Agnes, my old friend

I've come to play with you again

A cool new version of you just crept in

Left its cards while I was sleeping

While the version of you smiting with your pain

Still remains

It feels most sound with violence

.

In early days you walked alone

Signature cards that made us groan

That weakness gave your brain some cramp

Your Heirloom collar needed a revamp

That elder-sign never did much to excite

None of them quite

Work when you’re bound to violence.

.

And in your new Agnes I saw

Potential spell events galore

Grabbing clues without Rite of Seeking

Dealing damage without a Shrivelling

Spell events, replayed with their expenses spared

As few had dared

When you were bound to violence

.

Tools that I feel I barely know

Hypno Gaze now feels pro!

Hear my words that I might teach you

With a recurring HP soak or two

You can do this for almost all the game

...

Soaking all the pain... in silence

.

And then the people proudly played

The event spell machine they made

Your elder-sign gave out its healing

Your Heirloom makes sense when it keeps drawing

Dark Memory burns only horror that standing in full bloom

Making the doom

Safer, to delay, in silence

In the original Agnes, there are better cards for this slot, so you should probably play the Unadvanced version of the signature asset and weakness.

In parallel Agnes, this card is excellent, especially when paired with Scavenging (2) (using Parallel Front for Agnes, and Original Back / Deckbuilding for Agnes). This card can take the damage used with you ability to play spell events for cheap and with recursion. It can also take the occasional horror from Shrivelling, Clairvoyance, and every mystic's favourite Ward of Protection. Once it's use up, recur it back with Scavenging and go again, playing an endless supply of cheap events.

It's not clear whether the horror taken by Agnes' weakness can be placed here. When I played this, I assumed I could tank the 2 horror onto the Heirloom because the weakness has a player card back, not an encounter card back, and thus is a player card?

This is definitely a signature card worth building your deck around. There are of course other ways to manage the excess damage taken from using your ability, but this card providing a great soak-to-cost ratio, and allowing you to draw a card every time you play a spell (usually going to be an event), really does cement Parallel Agnes as a solid investigator option for your next game.