While its appearance suggests it is incorporeal, a hellcats has a corporeal body and can be harmed by physical attacks.
Hellcats use a natural telepathy to communicate with one another and those they encounter. A hellcat measures about 9 feet long and weighs about 900 pounds.

A hellcat can hold its own in combat thanks to sharp claws and wicked fangs. It prefers to leap upon opponents, just as a lion does.
A hellcat?s natural weapons, as well as any weapons it wields, are treated as evil-aligned and lawful-aligned for the purpose of overcoming damage reduction.
Improved Grab (Ex): To use this ability, a hellcat must hit with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can rake.
Pounce (Ex): If a hellcat charges, it can make a full attack, including two rake attacks.
Rake (Ex): Attack bonus +13 melee, damage 1d8+3.
Invisible in Light (Ex): A hellcat is invisible in any area lit well enough for a human to see. In a darkened area, it shows up as a faintly glowing outline visible up to 30 feet away (60 feet if the viewer has low-light vision). Magical darkness smothers the glow and conceals the outline.
Skills: Hellcats have a +4 racial bonus on Listen and Move Silently checks.

---

System Reference Document -> List of Creatures (SRD)