Tusk

Tusk is a phenomenal unit and has great stats in everything but fortitude, mastery, and luck. You have decent availability with him and he has pretty decent sustain if you have the vampiric glyphs on his skills. That said, while his combat ability is exceptional, I don't believe it is much more than average and he doesn't have any remarkable niches besides maybe Licky Lasso and Wing Buffet that anyone else in this class tree also has access to. 

Deadeye - If you want Licky Lasso, go Cuttthroat. Tusk doesn't have a great luck base or growth so only Licky Lasso and maybe 10-20ish dodge is all you'll get. Otherwise, Quickdraw Deadeye is pretty great as Tusk can hit doubling speed on some units innately and will have the mana back from quadding on something like the Repeater or any other bow with the Ferocity Rune to continue to spam his skills. His high HP will allow him to tank some hits and the Archmage Ring will allow him to attack safely from a distance on most enemies if he needs to recover with the Command Hyena skill with the Vampiric glyph on it.

Slayer - Again feel free to Cuttthroat for Licky Lasso. Additionally, if you have a spare Karambit, it will most likely perform better than a Cinquedea. Otherwise, enjoy the RNG and Tusk's massive might stat and respectable speed stat.

Tamer - By all accounts, Tusk does not have the base mastery statline to make this class feasible; however, Rings exists. The Heir Ring is Tusk's solution to his mastery problem by leveraging his massive HP to give him a free 10 mastery making him just shy of 30 at level 40. This will make him a very strong and bulky off tank, just as viable as the others in his class tree.