Mimics should try to impersonate containers more frequently than they do. There are a few proposals for accomplishing this in the Dungeons of Doom:

• Have a special case that generates a mimic in each room with very low probability per room; if a mimic does generate it will always imitate a chest or large box.
• When a large box or chest is generated in a room during level creation, there is a small chance it instead becomes a mimic imitating that type of container, replacing the box. However, the chest contents must be carefully discarded to unmake any artifacts that happened to generate inside it.

Both of these only happen on levels where the mimic being generated is within its ordinary level difficulty range.

A new mimic-class monster that can imitate an object (such as a scroll, potion, or wand) so deeply that it actually exists as that object, and you can pick it up and move it around without it revealing itself. It will only reveal itself, which destroys the object and creates the monster in its place, when you or some other monster attempts to use it (or possibly when it would stack with some other object, because an object that is a mimic clearly should not stack with regular objects).

Alternatively, just give this feature to small mimics.

Internally, this would probably work by generating a mextra struct on the object to store the details of the mimic.

When a mimic generates on a dungeon feature, they currently choose a random feature to mimic. They should instead always choose the feature on their square.

If you try to teleport or kick the swap chest too many times, it changes from an object to a hostile monster (a m) that is super strong, but if you somehow manage to kill it, it drops 2 random items that were inside it.

For every mimic you personally kill inside a shop, the shopkeeper gives you a token fee of 5 gold (or store credit) if you talk to him afterwards.

If you clear the shop of all mimics (with some minimum amount of mimics required), the shopkeeper could give you a free item of your choice.

Eating a mimic corpse typically makes you mimic some object besides a pile of gold, giving you an opportunity to identify it if you don’t already know it. You get the message “You can’t resist the temptation to mimic a [object]” with that object’s randomized description being appended if it was previously unknown.

The odds of getting an object you haven’t discovered are controlled by your Luck.

• If Luck is 0, you mimic the first random object type the game picks.
• If Luck is positive, the game rerolls up to Luck times to try and find an unidentified object type.
• If Luck is negative, the game rerolls up to Luck times to try and find an identified object type.

If you open a door that turns out to be a mimic, it “falls on top of you” and deals damage in addition to sticking to you.

Punching a mimic with a worn/wielded ring of protection from shape changers makes them die instantly.

Some pieces of armor may actually be small mimics, but they don’t reveal themselves until you’ve been wearing them for a while (at which point they bite you for high damage).

Monster which is a shapeshifter, but regardless of what form it takes it always has an engulf attack. This is because it’s actually a variety of mimic in its normal form.

Mimics can mimic corpses.

Some method to transform a mimic mimicking something into the actual thing it mimics. Possibly zapping it with a wand of polymorph.

Give all mimics acid resistance, because they have that in D&D.

Objects flying through the air do not interact with a mimic that is currently mimicking something; they just pass through as if it weren’t there.

Objects thrown at hidden monsters (whether the monster is hiding under something or an undetected mimic) pass right through the square as if no monster is on the square.

Mimics can mimic other pieces of furniture like sinks, thrones, and altars. (They can already mimic doors and stairs.)

Mimics are very likely to mimic chests, instead of random items most of the time.

Small mimics (but not large or giant ones) can mimic the floor, looking like nothing in the same way a trapper or lurker above does.

While you are on the ascension run, mimics prefer to disguise themselves as upstairs. It also edits your memories to make you think you remember the stair being where the mimic was (in order to fool the travel command routing to the correct upstairs anyway).

Shopkeepers should pay you a small fee for killing a mimic that was generated in their shop. (Or at least give you the corpse for free).

Sokoban prize closets that don’t have the prize instead have mimics that imitate the prize.

Mimics can pretend to die, mimicking a mimic corpse or appropriate death drop.