Kittens

 are passive kittens that sometimes randomly move across the screen. They do not take any lives, and are completely harmless unless provoked.

Details
They have a base HP of a random 30HP to 50HP, and both numbers are (exponentially) multiplied by 1.05 of every round passed.

After attacking a passive kitten, 3 to 5 aggressive kittens will come from all sides of the screen to attack your towers, but they will seek the offending tower(s) out. Aggressive kittens slash towers with their swords, dealing 3HP damage. Aggressive kittens also have shields that reduce damage by 60%, but have a 30% chance of falling off after hit.

Each passive kitten can only trigger the kitten backup once.

Kittens can come in any color, but are more likely to come in shades of brown, orange, gray, black, white, and blue.

Dropped Items
Killing kittens gives no actual reward, but they do give some items. The items in the exact color that the killed kitten's fur is, and all of the different colors of kitten drops can be viewed by right-clicking the item.
 * Kitten Fur: 2 to 4.
 * Kitten Ear: 20% chance to drop each.
 * Kitten Tail: 30% chance to drop.
 * Kitten Sword: Only dropped by aggressive kittens. 15% drop rate.
 * Kitten Shield: 25% chance to drop when a kitten loses its shield.
 * Kitten Essence: 4% chance to drop 2 to 4.
 * Kitten Soul: 1.2% chance to drop.

Results of killing Kittens
Killing kittens has long-term negative side effects.

Trivia

 * These are kittens from Epic Battle Fantasy 4.