Tornadus (Incarnate Forme)

The first member of the Forces of Nature... exists. A very unspectacular moveset cripples its ability to compete against other Flying types, despite its respectable ATK stat. Beyond this, it's never going to top the Flying charts with monsters like Mega Rayquaza with Dragon Ascent running around. On that note, Tornadus - Incarnate Forme has access to Bleakwind Storm, but only during special events and not via Elite TM.

Best PvE Offensive Moveset

• Air Slash is the way to go by way of Fast Moves.
• Bleakwind Storm* is the best option by a large margin here, but its rarity means that Hurricane is the way that most will go.
• Bite and Dark Pulse can make for a Dark Type attacker, though it's not good in that role.
• Grass Knot and Hyper Beam are not worth considering on Tornadus.

Air Slash takes advantage of STAB and provides decent energy generation. Bite can be more preferable depending what coverage is needed, but the lack of STAB and very poor energy generation makes it less optimal overall. 

Bleakwind Storm* is optimal due to its low cost and debuffing capabilities, but its rarity makes it a bit rare on Tornadus - Incarnate Forme. Grass Knot is a strong charge move and covers Rock-type Pokemon that Tornadus is weak to, along with common Water Pokemon. Dark Pulse provides relatively neutral coverage against various meta picks across all three leagues, but can be particularly useful in formats such as Open Ultra League. Hurricane is quite strong with STAB, but has an expensive energy cost that Tornadus can't generate comfortably with its fast moves. For that reason, Hyper Beam is also not recommended.