@Background Pony #3529  
The Sphinx was a prize for defeating her specifically in the third round in a very short time. Like if you look below:
 

 
there’s an upper timer for the whole event, and a lower timer for just that round of the Sphinx fight. You would have 5 days and 9 hours to win the event (or at least in round 2 here, Hissan’s palace), but only 1 day and 17 hours to win the Somnambulan pony (or in round 3, the Sphinx) too. So you could have maybe finished the event with 12 hours to spare, but didn’t win round 3 fast enough to get both prizes.
 
If you got Prince Hissan but not the Sphinx, unless you’re sure you still had time on the lower timer too, that’s probably what happened. If you got neither, or are certain you still had time on the lower timer (I think that meant winning the third round in less than 2 days and 12 hours from the end of round 2) then try contacting tech support.

Cute ear twitch by the Sphynx

I managed to defeat her, but I didn’t get the character. I’m thinking it was a glitch or something. I had like, 12 hours until the event’s over.

RIP she had 50 health and I had 1 hour to get her

I really like this Sphinx character. She’s connected to Egypt and she’s a villain

I’m so close to getting the sphinx but I don’t think I’ll make it in time :(

I’d love to see this happening in the show.

@Cyborg_pony  
Sphinx cast Riddle Talk
 
Fluttershy becomes confused

Fluttershy casts: STARE
 
SPHINX is stunned.

She’s so unsettled! XD