I bought this two months ago.
Unfortunately it seems that about a quarter of the flan was broken off in antiquity, so the last part of the obverse legend is missing and part of the year date (LK) on the reverse is missing, as well as a chunk out of Cerberus.
Giving it some attention, I noticed how the style of Commodus' beard resembles more the style seen in the later busts of his father, Marcus Aurelius, and imitated by Septimius Severus, like "icicles" as Furious Rufus would say.

Most of the Billon Tetradrachms of Commodus that I have so far aquired have his beard quite short.
Here is the info on it:
Obverse: MA KOM ANTω - CEB EVCEB, laureate bust facing to the right.
Reverse: Serapis, seated to the left, holding a sceptre with his left hand and his right hand over Cerberus, seated to the left. LKΘ in the upper left field.
Weight: 9.90 g, Diameter: 22 x 25 x 3.2 mm, Die axis: 0°
Mint: Alexandria, year 29 (LKΘ),
struck between 188 -189 A.D.
Reference: Milne 2680
