As they are now, Treasure boxes are....dull. You could maybe get a bunch of crowns, or even an item from one, but they're nothing special. Just sources of loot.

I propose a new type of enemy: treasure box mimics.

There will be three varieties: Green Jelly mimics, Green Construct mimics and Red Fiend mimics. They'll look similar to normal boxes (with subtle differences) and can spawn in the place of any given Treasure box, perhaps with 1/4th chance a Stone Block has of becoming a Rock Jelly.

Since I lack artistic capability, I'll give you a reference picture, taken from the game Dark Souls.
http://images1.wikia.nocookie.net/__cb20120118034615/darksouls/images/4/...

In Dark Souls, Mimic chests look slightly different than standard fare loot chests (a chain next to them is turned the opposite way). Attempting to open one of them would result in your character being eaten alive by the mimic. Kicking or attacking the mimic would cause it to grow legs and arms and open its mouth, trying to turn your Lost Undead into its next snack.

Mimics, like Drones and Battlepods, take neutral damage from every source, to not mercilessly screw anyone who encounters them. Mimics of both varieties also drop a lot of hearts, enough to patch you up a scaled amount. This amount will be three hearts in T1, seven in T2, and 10 in T3.

I'll extrapolate on this later, but these are what I have now:

Green mimic: Spawns in place of a Green Treasure box. Attacking it causes the mimic to sprout thorns and rush your knight, much like a giant lichen colony. Health would be 4 times that of a normal Giant colony, and killing it would yield a large amount of crowns, heat, and other fun stuff.

Other Green mimic: Spawns in place of a Green Treasure box. Attacking it causes the mimic to transform, Transformer style, into a Scuttlebot. The Mimic has three primary attacks: Strong Retrode laser (think Five star Brand), chopping anything that gets too close with rotating blades, like Hyneman's Blendo, and at low health, shutting in and regenerating, akin to a Gremlin Mender. While regenerating, beating on the mimic will wear down the shield, and possibly break it if enough damage is dealt. Yields same amount of loot as Green Jely mimic.

Red mimic: Spawns in place of a Red Treasure box. Attacking it causes the box to grow legs, arms and a curse eye. Attacks with zombie swipes, firing shadow projectiles from its eye (Think Devilites), and at low health attempting to grapple and eat whatever's in front of it. Mimic will also be highly evasive, dodging left to right randomly. Will have 4x the health of a similarly tiered Trojan, and on death yields a truly massive crown yield (4-10 Gold Coins) or in extremely rare cases, an item.