I remember we've had threads about mimics before, but I thought this was a bit different.

You have the little treasure box and it moves around a little, but stays in the same place. Sort of just jiggly moving.

When you break the box, underneath is a little Solid Snake Jelly, kind of a grey-blue colour, with a headband on and a smoke poking out of his somewhere.
Maybe some manly facial hair.
You can't tell me you don't know what Solid Snake looks like.
Also, a little exclamation point appears above his head with the obligatory alert sound.

Instead of a round core he has a combat knife that pokes out the side when he spin attacks. He moves a lot faster than other jellies and once out of threat range, he will hide in a box again.

Breaking the box doesn't damage him. From close range (swinging at it), he will attack you almost instantly.

When he dies, he explodes like the other jellies. But the knife spins in the air before coming down and sticking in the ground, in the centre of where the headband is.

His trademark item could be a communicator trinket with the description: Snake? Snake?! SNAAAAAAAAAKE!
Offers up some kind of sword damage bonus or something.
If you still plan on having trinkets, that is.
I don't know what's going on with this game.

There are any number of terrible pun names for this guy and I'm too lazy to think of them all by myself. You guys can do it if you want, I'm pretty bad at it anyway.