I love sharks, and am justifiably terrified of them. So what's not to love about the wereshark? Here is a version statted for Labyrinth Lord:
No. Enc. 1d4 (1d4)
Move: 120' Swim 180'
AC: 2 (8)
Att: 1 (bite)
Hoard Class: XX
The dreaded wereshark is the result of a form of lycanthropy that allows the creature to assume great white shark form at will, so long as it is in darkness. Thus the wereshark has a great white shark form (see LL p. 95) and a human form. The first AC number listed above is for its shark form, the AC in parentheses for its human form. As a lycanthrope, the wereshark can be affected by magic or silver weapons only (see Lycanthrope, LL p. 85).
[Inspired by the "Wereshark" entry on p. 82 of the Monster Manual II by Gary Gygax.]