The mimic spits out a magical Dire Chicken (breed- Brahma). when you chop this chickens head off a new body will grow from the head; this chicken cannot be killed outside of being dropped into a giant fryer. The body left behind can be used for food. This chicken will not feel pain and will not resent you for cutting it's head off. Also it can breath fire and can use it's fire breath to cook it's old body for you.

I feed the mimic the head of Baba Yaga.

Miss mimic stares at the head,then looks at the headless chicken body, then back at the head, before she puts the head on the chicken body.

I hand over 'Dr. Frankensteins guide to making your own Monster'.

The mimic reads it, rereads it, and writes an elegant, eloquent treatise on the subject of why Dr. Frankenstein's methods would never work properly. 

I feed the mimic a khopesh. 

The mimic spits out gold leaf.

Quote from AcerakTheEternal >>

The mimic spits out gold leaf.

I feed the mimic a bullfrog.

The mimic, angry at being neglected, spits out a fireball - right in your face.

I feed the mimic a 12-step program book on overeating.

It thanks you by making you dessert (your the dessert).

I feed the mimic a spell scroll of stinking cloud

It burps out a stinking cloud and your disgusted

I feed the mimic the gnome ranger

The gnome shudders slightly, and then a copy of the gnomes crossbow grows out of the chest's lid!

I give the mimic a quiver of crossbow bolts.

It chews for a bit then spits the bolts out in your face doing  5 damage.

I feed the mimic  a mimic.

The mimic didn't like this other mimic so it decides to give you its tongue

I feed the mimic a weighted d20 

The mimic spits the die back out, and rolls a 2. It demands a good d20.

I feed the mimic a decent, non-weighted d20.

The mimic rolles the dice. And gets a 1. The mimic is very angery and throws a beef n bean burito at you.

I give the mimic, a saxophon.

The mimic spits up a bracelet with different tiny instruments that plays only smooth jazz on command.

I feed the mimic a bunch of HG Gundam, and Robotech/ Macross models

It never liked those and eats your arm

I feed the mimic Dwight Schrute's bobble head 

..... The Mimic doesn't like it or Dwight Schrute and eats your head; you die...

I feed the mimic a bunch of Lego Bionicle, lego Technic, and lego Mindstorms stuff...

It spits out a Lego robot with Artificial Intelligence. We are now one step closer to the world being taken over by Lego robots.

I feed the mimic Microsoft Word.

The mimic spits out a large paperclip with goofy googly eyes under the permanent effect of the Tiny Servant spell. It will do all paper work and write all reports you tell it to do and generally act as a servant. It will also magically fix all mistakes in your writing and work automatically (even if it is the fault of spell check or another person).

I feed the mimic a bunch of Dragon Ball and Dragon Ball Z stuff including Dragon Ball FighterZ.

The mimic grows large spiky blond hair. And prosedes to give you a hyperbolic time chamber.

I give the mimic a roll of hyper absorbent toilet paper. Only the best for the mimic.