Intelligence
Weight
Small size
Step 1: Identify the subject and key information
The question asks about the specific characteristic for which the Halari donkey, an endangered breed according to IUCN, is known.
Step 2: Recall or research information about the Halari donkey
The Halari donkey is a rare and endangered breed native to the Saurashtra region of Gujarat, India. It is primarily known for its distinctive intelligence and gentle nature, which makes it suitable for various tasks and easy to train.
Step 3: Evaluate the options
(1) Height: While height is a characteristic, the Halari donkey is not particularly famous for it.
(2) Intelligence: This aligns with known information about the breed's temperament and utility.
(3) Weight: The Halari donkey is not specifically known for its weight. (4) Small size: They are generally medium-sized donkeys, not particularly noted for being "small sized" as a defining characteristic. Therefore, its intelligence is the most distinguishing characteristic among the given options for which the Halari donkey is known.
The final answer is $\boxed{\text{Intelligence}}$.