This is something that happened on an account of mine a long time ago, which is why I made another. At some point, the "Creature" button simply went missing. I have no idea what caused it, or what I did before it happened. The result was the following: I could not manage my creatures, and I could not attack anyone; I could, however, sacrifice them, and once I sacrificed one, I was able to buy a new one - when I did this, the creature button reappeared. My guess is that there was a update of the game in between the periods of time. In any case, it got fixed, but only through sacrifice.
This occurred on the following character: Asthazar (ID:154350; Days:14)
P.S.: The following is not a bug; more of an observation, so I don't want to create a separate topic for it.
In the MDA, in the Great Hall of the Sun, when you go through the entrance to the left (or right, if you turn the picture around to fit a x,y perspective) you end up in the Maintenance Access Stairs (part 1) which have the stairs going up on the right wall. Once you climb the stairs you reach the Maintenance Access Stairs (part 2) which have the stairs going up on the left wall. The artwork is reversed. :P This could be explained if there was a series of stairs one went through from part 1 to part 2, but I thought it wouldn't hurt to mention it. :P