According to Smogon, the IVs can be any of the following:
Hidden Power Fighting:
31/O/30/30/30/30
30/E/31/30/30/30
30/O/30/30/30/30
30/E/30/30/30/30
The Os represent the odd values of 3, 7, 11, 15, 19, 23, 27, 31
The Es represent the even values of 2, 6, 10, 14, 18, 22, 26, 30
In a Trick Room Setting, the a 30 in speed would be replaced with a 2, while a 31 in speed is replaced with a 3.
These are the values that will get you HP fighting on your Cofagrigus.
I Hope I Helped!
(Sorry if I posted this late/got sniped)