First, the tl;dr: For a bleeding-edge speed run, the stocking mimic has negligibly small impact on softcore, but will save around 3-4 turns in hardcore. For runs where the player is missing key skills or Mr. Store items but is still trying to go fast, the impact might be as high as 10 turns. However, in either case, the tradeoff of using the stocking mimic is increased RNG swinginess.

Ascension analysis

Given that it is never optimal to use a cocoabo in a speed ascension, and the mimic is identical to a cocoabo except for the candy drops (the weight cap is irrelevant, as we won't be coming close to 20 pounds during the ascension), this analysis will be based mostly on the candy drops.

Softcore

Turns spent with the mimic in softcore would be replacing the bandersnatch. It takes, on average, 18 turns to get one of each candy, so costs you 18 * sqrt(weight) mainstat. In a typical 2-day run, a bandersnatch will see 225-280 combat, which will get it up to 15 pounds; another 20 pounds comes from +weight skills and the jubjub bird, for a total of 35 pounds, or about 108 mainstat in 18 adventures. Meanwhile, the mimic drop gets 10 adventures of +level stats, but potentially loses turns to non-combats. Optimal play with the mimic, then, is a zone with 100% combat rate and use of the buff at level 11+ (HitS/battlefield); this is 110 stats * 100% / 2 mainstat, or 55 main stats.

Even if we tilt the assumptions in the mimic's favor (bander only 10 pounds base at use), that's still a difference of nearly 43 mainstat in favor of the bandersnatch, plus those stats come earlier, when they're more important. Also, these are raw stat gain; the difference is magnified by 25% due to all the turns for an optimal SC run being played on stat days. A 43-53 raw mainstat difference is more like 54-66 on a stat day, and worth something like .6 turns in favor of the bandersnatch.

Now add in the +item/meat drop. Assuming a best-case scenario of +255% item drop and a 49 pound hound dog, an extra 55% item drop from the polka pop will save less than 1 turn, and so is barely worth getting, since it costs .7 turns of stats. The best-case scenario for the nuns looks slightly better; at 340% meat drop and a 44 pound hobo monkey, a polka pop will save roughly 1.2 turns, or a net of half a turn.

Given the very small turn savings and the possibility that using mimic will actually cost you turns if it takes longer than expected to get your polka pop to drop, for softcore runs I'd plan on leaving the mimic in the terrarium.

Hardcore

In hardcore, the analysis looks similar, except that the mimic would be replacing a non-tuned volleyball or a sombrero; additionally, familiars tend to be of lower weight, since there is more familiar switching required. Also, in hardcore, the mimic can be run on a non-stat day, while the candy can be used later, on a stat day. We'll use the following assumptions: 160 ML, 100% combat rate, 20 pound volleyball or 30 pound sombrero on non-stat days, using the candy at level 11 on a stat day. This works out to 62.5 stats for the mimic, 40 stats for the volleyball, and 66.5 stats for the sombrero.

So, if you can run it early enough that it would replace a volleyball, the mimic gains .2-.3 turns on stats; the item/meat analysis looks pretty similar except that an optimal player will likely have an additional 60% item drop and 60% meat drop. Plus, the cocoabo effects of the mimic are more important in hardcore as there are fewer ways to make combat easier with equipment, and of course generating MP/meat is always a challenge. Call this about a turn's worth of savings.

Using a pattern of pulling out the mimic as early as possible while still hitting consumption goals (ideally on day 1 or 2, immediately after your llama drops 3 gongs, before switching to a bander for the day) and getting 2 polka pops, I'd estimate something like 3-4 turns saved using the mimic in hardcore.

Aftercore

I won't go into the details of an aftercore analysis, as a great deal of the mimic's marginal value is tied up in the mall price of the candy it drops (and that price may be affected by the publication of any such analysis). However, suffice it to say that the mimic is probably not worthwhile purely for farming purposes unless you:

- spend a LOT of time in aftercore each ascension (on the order of multiple months), OR

- spend many turns per day in hobopolis or another zone with no meat or item drops, don't have another familiar that drops valuable mall-sellable items (llama, sandworm, badger), and can stasis for 10 turns, OR

- can convince everyone else to stop selling polka pops.

Keep in mind that even if you can do one or more of these things, it will take some time for the initial investment to pay off. As such, I wouldn't recommend buying a stocking mimic just for aftercore farming, though if you decide to buy one for ascension purposes, there will be times when you can pull it out to make a wee bit of extra meat.

FAQ

- I don't believe these numbers. What do you mean by "best-case scenario"? For item drop, I assumed 3 unicorn stickers, fat loot, MLS, ballroom song, plexi pants, 4+ songs of disturbing obsession, lavender candy heart, mining helmet, knob eyedrops, hobo/gnome passives, and either Jr's (softcore) or raven feather and roachform buff (hardcore). For meat, I assumed 3 UPC stickers, winklered, polka, demon, pink candy heart, 4+ songs of sugary cuteness, 4 passives, 1 inhaler, and a buzzard feather (hardcore only). For familiar weight, I assumed sympathy, empathy, leash, pet-buffing spray, green candy heart, a base 11 pound hound dog and base 1 pound hobo monkey plus sugar shield; I also included the feast buff and a 5 pound feast bonus for the dog.
- OK, sure, but this is all theoretical, right? The fastest HCNP run in NS13 history, Exactor It's 3/809, used the mimic for 33 turns, right about what you'd expect it to take to get 2 polka pops.
- What about non-optimal situations? (No bandersnatch, no Jr's, no +item/meat skills, no +weight skills etc.) The mimic's benefit is almost entirely in the candy drops, which are dependent only on player level. The opportunity costs, however, are dependent on +weight, +item, and +meat, which are given by skills and shinies. Therefore, the fewer skills/shinies you have, the better the mimic becomes. In fact, even for a player with a full suite of skills and shinies, poor RNG elsewhere might make pulling out the mimic a good choice: if, for instance, in a softcore run, you get only 1 UPC sticker, don't acquire an AFUE scroll, and get no songs of sugary cuteness, a polka pop will save you a little over 2 turns at the nuns.

In extreme situations (no skills, no shinies), a polka pop might be worth as much as 4-5 turns at the filthworms, and about the same at the nuns (though it's a little bit complicated to figure out exactly how much, since the conditions under which you'd achieve maximum savings at the nuns would imply that it would be optimal to simply skip them), plus give a good way to deal with physically resistant monsters. - What about suitability for 100% runs? Well, let's see. You get MP/HP in battle, plus stats and item drop from the candy. It may not be optimal, but it'll give you a bit of everything you need, and provide some strategic options for managing it. Anecdotal evidence seems to indicate that 100% mimic runs are fun and not at all painful.
- I'm a casual player. Will I like the mimic? While you'll get the most benefit from the mimic by using the drops at the right times, you can get a lot of the benefit by just using them whenever. It doesn't require a whole lot of careful management (see: absinthe, gongs, bander runaways), so seems pretty suitable for a casual player.
- What about flavor text? Is it fun? Will I love it and huggle it? It's got boobs and it drops candy. What else do you want?