[RPG] Can a Mimic (container form) actually hold loot

I am having the same problem, although my characters just reached level 3.

However, I think that the best answer is for the party to better share the loot between each others. They, after all, are the ones who want to survive, not you.

If you have one player who always takes it all, he will create the imbalance, not you as the DM.

For what to "distribute", I use the tables on DMG p. 136-139. That gives me a way to determine the various types of objects I can give my players. The main problem is to avoid giving them way too powerful items.

However, I do not like to roll on the tables because I prefer to be in control to give the players exactly what they are likely to need (plus a little more).

Also, there are certain things that make sense. If you kill a mummy, it makes sense to find a Staff of the Python and if you kill a Wizard to find a Robe of Stars, for example. Plus, I prefer to offer items that make sense in the adventure rather than random things.

That being said, there is one rule that will limit a player from using all the items. If you look closely, there is a rule about attunement (DMG p. 136) which prevents a user from having more than 3 items that require attunement. So if you offer many of those, the one player who wants it all... would not be able to use the extras and may then start thinking he should share a bit more (because such items in his backpack won't do much good to the group as a whole.)

Another way to limit is to give similar items or items that the user(s) do not have proficiency in (i.e. give 3 short swords + 1, it is likely that people will stick to their existing weapon because they don't have proficiency in short swords. That being said, they'll need magical swords for killing those werewolves...) Also you cannot use two magical items of the same type simultaneously (DMG p. 141). So that's another way. Obviously, that could become quite a bit monotonous... but it could be a temporary solution to get everyone to have a similar power level. And the characters can sell or exchange the extras too.

Finally, there are items that require a specific class or set of classes (see Staff of the Adder, DMG p. 203). You could also impose limits such as race or size or even level... since you do not have to specifically use what the DMG presents. I myself use it as a large set of examples rather than the actual source of magic items in my worlds.

No,

Mimics can only strictly turn into objects, that means things like, doors, door frames, key holes, keys, key rings, door knobs, knockers, peep holes- and those are just the door-and-other-doory-objects Mimics.

But...

Since a dead creature is considered an object, they can turn into a dead creature, if you want. It should be noted that they don't get the creature's stats and attacks.

Creatures that shapeshift

There are many creatures that can assume the form of humanoids and beasts without casting spells: Metallic Dragons and Deva, come to mind. I won't list them here but you can look through the Monster Manual to find the ones with the "Shape Change" trait.

A creature that can cast Shapechange is also a good candidate for what you want, it is, however, a 9th-level spell.

However, it appears what you want to be able to do is to make the mimicking creature appear stronger than it actually is. Most creatures with Shape Change can only look weaker, one exception could be the Doppelganger- taking the form of, say, an Assassin.

For Beholders, specifically...

There is a fungus called Gas Spores found in page 137 of the Monster Manual. They can serve the purpose of mimicking Beholders, as they are described as:

A gas spore is a spherical, balloon-like fungus that resembles a beholder from a distance, though its true nature becomes increasingly obvious as one approaches it.

Have fun freaking out your party!