Borran Klosk (from Forgotten Realms: The Jewel of Turmish by Mel Odom) is not an average mohrg. His tongue alone is one nasty weapon. It can shatter bone, wood and break stone. Borran can also cast spells. Has anyone ever made a stat block for him? He'd be a fun villain to run with.
Should be simple enough. Add damage to the tongue and adjust CR accordingly via the monster creation guidelines. Toss in some caster class levels, replace a few existing hit dice with them, or just drop them in with a predetermined CL and wing the CR.
A spellcasting mohrg. What'll they think of next?
Edit: Oh hey, there's already the demonic mohrg variant on the SRD. It's a start.
Dunno the character at all, but you might try the Dread Mohrg template from Green Ronin's Advanced Bestiary (for 3.5). It's tongue can deal damage as a natural weapon in addition to delivering the paralysis. There's a conversion of the template here:
http://www.d20pfsrd.com/bestiary/monster-listings/templates/dread-mohrg-cr- 2