Keen smell. The dire sheep has advantage on saving throws based on smell.

Herd awareness. If the sheep is within 15 feet of another sheep, it can not be surprised.  

Pack tactics. The sheep has advantage on attack rolls against a creature if at least one of the sheep's allies is within 5 feet of the attacked creature, and the ally isn't incapacitated.

The dire sheep can make two headbutt attacks, and one trample attack per round. 

Trample. The sheep gallops in a 15 foot line over up to 3 medium or smaller creature that are prone: +3 to hit, requiring a DC 16 dex check to avoid it. Hit: 16 (4d6 + 4) [bludgeoning] damage. 

 Headbutt. The sheep rams its head into one creature: +5 to hit, range 5ft.,  
Hit: 12 (2d10+2) [bludgeoning] damage. The creature need to make a DC 16 strength check or be knocked prone.

Renewed Strength. If cornered and below half health, the sheep panics and gains 2d4 hp. This feature can only be used once a day.