What does Rick kill in 'Auto Erotic Assimilation'

A quick review of episodes shows that we haven't seen this creature before. From the fact that it begins the episode in stasis, it can be inferred that

1. this creature has been in stasis for some time
2. the creature appears to be in distress when unfrozen

We can assume that

1. the creature was placed in stasis to pause the pain
2. this may have been Rick's fault (possibly a failed experiment)
3. Rick may have planned to unfreeze the creature at some future point when he could solve the creature's pain

Due to his huge ego, we can assume Rick believes himself to be the only one who could stop the creature's distress. As Rick obviously plans to commit suicide, instead of leaving the creature in perpetual stasis, which one can theorize might wear off at some future time, Rick puts it out of its misery. Killing the creature demonstrates to the audience that he has given up; backed up by his own failed attempt at suicide.

In pop culture, this concept of preserving a problem to solve at a later date is reminiscent of both Superman's "bottle city of Kandor" (a miniaturized Kryptonian city he has vowed to save) and Mr. Freeze's wife, Nora (who is frozen until a cure for her fatal disease can be found).

It's a Cronenberg baby from the earth that Rick and Morty left behind. You can tell because it has a human skeleton and looks similar to the other Cronenbergs. My guess is Rick froze it to try to find a way to reverse the Cronenberg mutation, but unable to do so, he now puts it out of its misery.

I have a feeling that the creature was the original Morty. The Morty that Rick started with. If you remember the Council of Ricks gives Rick a replacement Morty coupon to apologise for accusing him of killing the other Ricks. This tells us that Mortys die regularly enough for that to be a 'thing'.

Rick is the pure equivalent of chaotic evil. That doesn't mean that he doesn't have feelings for his family but they're abstract. As long as he has versions of them he couldn't care less.

So that's why for the first time we see Rick sad and actualy being gentle with something. The original Morty. His Morty. Beyond helping with all of Rick's genius.

And when that Morty is gone so is the last of Rick's real family. He's truly alone.

The more I look at the episode, the more I think there could be something to the theory that it is either Rick's original Morty or another family member.

The first time we see it, Jerry picks it up in the middle of his argument with Beth and asks, while holding it, if Rick will just go live with "his other family" (rent free). From a storytelling standpoint, this is significant since that version of the Smith Family is not Rick's original family. As we know, the show starts off in a timeline that is eventually "Cronenberged." So we know that Rick has that family out there —with whom he was living without paying rent and what not— and there's nothing in the story to suggest that the Smith Family in the Cronenberged timeline is Rick's original family either.

If the storytellers didn't want us to make that connection, then there would be no need to make a point of showing the creature at that moment. Or at all until Rick was going to put him out of his misery. Maybe it's his original Morty or just some previous Morty. Perhaps it's his original Beth. Maybe it's his original wife. The Cronenberged world is the result of Rick creating serums that manipulate people's emotions. With the amount of disdain Rick has for marriage, it's possible that he previously attempted to chemically manipulate someone's emotions (hence how he knew that it would be a problem if the solution were used on someone who had the flu) and that person was turned into a tiny little Cronenberg.

Couple this with the fact surface observations that it is an ugly little creature which Rick has kept hidden from everyone that seems to be in a pain that can only be alleviated by death and you have a metaphor for Rick's personal suffering/essence. Symbolically, that's Rick's tortured soul deep down: in the episode he's not confronting the reality of who he is and what he's doing (how destructive it is) and how he's numbed himself (like the freezing) with his exploits. Additionally, as a frozen statuette, the creature (presumably) feels nothing. Rick pours a solution on him and he begins to feel the pain of his existence. Then Rick drinks the same concoction, the implication being that in his last moments, Rick would not have been number but, instead, immersed in the weight of all his pain.

To condense, it could be a.) no more deep than what we see: a little Cronenberg from Cronenberg world that Rick saved, perhaps with the intention of reversing the process (after all: the minute it happened in Rick Potion #9, Rick immediately had a name for what was happening, suggesting that perhaps he'd done that before) or b.) is a symbolic truth based on what we see: a representation of Rick's pain and suffering that he's kept tucked away and an embodiment of his intention to end his own suffering or c.) a contextual mystery: a person we know, likely a member of Earth Rick c137's actual family.

Earlier in the episode, the conversation with the alien with his daughter and Jerry, it's implied Rick only wants to create a cure for his own financial gain.

The purpose of the frozen creature was to show that Rick loved this creature, and was trying to cure it. He's not keeping the creature trapped purely out of greed and selfishness. That was the entire point of the episode. Rick's inability to be unselfish in his relationship with Unity inevitably leads to her leaving him, even though in his heart he loved her very much.

The little guy is a Kronenberg. Watch for the human skeleton when it is zapped. It's Rick letting go of his timeline in which he turned everyone to a Kronenberg, remember Rick and Morty are from a different dimension at this point. Could be nobody or any of his family, maybe the first Unity even.

Whenever I see it, I get some serious feels lol. But besides that, I keep thinking that it may have been some kind of gift from unity. While I understand people's theories about it being a failed experiment that he froze to look at again on a later date, I believe that the way he treats it says something else.

Here's my theory:

Rick and Unity used to be in a relationship and it could be possible that the creature was a memento from unity or could be a memory from their past relationship, which could explain why Rick petted it and tried to calm it before he killed it (apart from him feeling depressed and about to kill himself). He may have frozen it because he still had feelings for Unity and did not want to get rid of the creature yet and be irrational.

This time however, Rick may realize that he and unity will never truly be together, and that he is once again without someone that made him feel happy and was one of the few people he genuinely cared for which everyone knows that, for Rick, that is a rare sight. Anyone has serious emotional feelings after a break up and would consider suicide, but Rick must have felt it more than most and acted so quickly (while also being an alcoholic). So this time, he didn't want to chance it and got rid of this "gift" from unity and be done with himself.

I just saw a compilation video of end credit scenes for season 2 and in the episode right before this one, where rick and Morty hung out at the arcade, the end credit scene shows an array of arcade food, including a bunch of those little monsters slathered in sauce and on a stick. So, the little creature is Rick’s leftovers that he froze. Edit: hm, maybe not. These ones have a bunch of eyes.

It was a part of Unity that Rick kept with him saying that was the only person he really loved. Look at the eyes of the creature same color. We've never seen Rick show real emotion till now.

I always theorized it may have been Rick's and Unity's child...being a hive mind and most likely inhabiting an alien species maybe they attempted to have a child and the result was the poor thing Rick showed so much emotion for...

Look at the series, Rick is a cold blooded scientist first but even with that in mind his treatment of Beth is always a little softer than anyone else, referring to her as sweety and giving compliments to her (for Rick that's huge) so maybe their child born in agony, of two parents who should have been separated by light years of space...

Maybe he held onto this child maybe not even to cure but because he couldn't bring himself to actually kill it... until unity broke him and Rick decided that the time had come for their child and himself...just a thought.

I think this Rick is a Cronenberg Rick that was transformed into a human Rick because of a disaster similar to the one on the episode "Love Potion No. 9" (call back to the hidden clip after the credits). And that this little thing is some small child (maybe his) or an animal that he froze rather than abandoning when he was transformed into regular Rick and couldn't fix himself. He kills it so that when he commits suicide, it won't be in perpetual suspension (as described by JoshDM).

I think that this thing was unity. Unity can be any person. So maybe the pretty unity is just a alien she was infecting first or so. So he killed the original unity resulting into every single unity dying.

The creature was sadness incarnate. Rick froze it to try to cure sadness itself later but in his dispair he thought the only way to cure sadness was to kill it because life is sadness.