Yes , i have a Gastly lvl 12 ( just found it wild) and it has mean look
There is no Mean Look TM in diamond
Any ghost type Pokemon can learn it.
Golbat uses mean look in Pokemon pearl but i am not sure about Pokemon diamond and pearl.
There is no TM that contains Mean Look inpokemon diamond. You need a Golbat if you want mean look
The moves Block and Mean Look do not exist as TMs on Pokemon Diamond. Block and Mean Look have yet to become a TM in any of the Pokemon games so far if ever.
Crobat
if you mean:wich Pokemon know mean look? you can catch golbat at level 45 in mt.cornet.
The questions are only Water, Fire and Grass. There is no ghost
Dark and ghost
you teach a Pokemon that move or use a TM
GOLBATI think you can get a golbat or crobat to learn mean look in Pokemon diamond/pearl. you can get golbat almost everywhere.
Crobat can learn Mean look, and there are a few others that I forget.