Museum of Natural History (Currently)
This Egyptian cat is an exhibit that appears inside a painting of Ancient Egypt, which is seen in the Metropolis Art Museum, in Night at the Museum: Kahmunrah Rises Again. They appear towards the middle to end of the movie, being a minor character yet, still being present for the rest of the movie with Octavius and Jedediah.
Appearances
Night at the Museum: Kahmunrah Rises Again
In Kahmunrah Rises Again, this exhibit does not actually appear until the end of the movie.

The first time we see this cat is when both Jedediah and Octavius slide down a hole and land on the ground, leading the cat to walk up to the pair and hiss at them, leading Jed and Oct to scream in fear. Not too long later, since the screen had cut back to the main action, we see the cat hiss at Jed and Octavius once more. This leads the pair to scream in a high pitched voice before the cat hisses once more, using it’s claw and swiping at the pair, trying to attack them. Though, the cat then is seen cowering away in fear before stepping back, revealing that a copra is in the room with them. The cat quickly recovers from it's fear, hissing at the copra as the scene cuts out once more.

When we cut back into the scene, the cat once again hisses at Jedediah and Octavius (which the cobra does the same), being trying to attack the pair once more but failing to land a hit. Though, the cat does not attack when Octavius and Jedediah team up against the cobra, instead, it waits until the cobra has slithered away to do anything. This is where the cat seems like it is getting ready to attack the pair, but it instead leans down and licks both of their faces as it purrs.

We don't see the cat until Kahmunrah is about to push the last button on the tablet to summon his undead soldiers, in which it's hiss is heard before it flies out of a hole in the building, having Jedediah and Octavius on it's back as it attacks Seth, the God of chaos. Once it does that, it jumps down and joins Nick and the rest of the exhibits with him. When Kahmunrah's undead soldiers start to attack, we see the cat run underneath their legs, with Octavius using his sword to attack the soldiers while Jedediah uses his lasso to take them down as well. Due to the overwhelming amount of soldiers though, they get surrounded.

Since Nick had thrown his flashlight, which leads the other exhibits to do so, Jedediah and Octavius hold onto the flashlight with Jed's lasso as they attack a few of the soldiers, in which we see the cat standing and letting the pair do so. Then, they all group back together before Seth uses his powers to separate them once more. When the group gets back together, we see the cat with everyone else- overall being a background character once more. Still, later on when Kahmunrah and Seth had been defeated, we see the cat looking at Jedediah with curiosity before it looks 'disappointed' in a manner due to his joke of relating Kahmunrah to Ancient history.

Once they run outside due to the temple that they were in starting to falling apart, we see Jed and Octavius getting off the cat, with Jed petting the cat as the sun rises. With the realization that they will all turn to dust, Nick manages to come up with the idea to use a poster as a portal to get out, leading them to build it and the cat going through, now becoming an exhibit to the Museum of Natural History. Once there, Jed and Oct say their good-byes to Nick, Jedediah tells the cat to- 'giddy up' before it ran off, not to be seen until later. When we do see it again, it is thanks to Dr. McPhee pointing out the cat randomly being in the middle of the hallway but rolls with it, instantly liking the cat and stating how he'll order clothes for it.
At the end of the movie, the cat is seen walking to the beat of the music, which is playing due to a dance party, before letting Jedediah and Octavius off it's back and then letting them back on it's back once more- then walks off.