@Jeehbs >
http://dnd5e.wikidot.com/feat:great-weapon-masterOn your turn,
when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.

So, can anyone confirm the extra attack as a bonus action with Great Weapon Master?
I believe it should ...
You still have only one Bonus Action tho ...
Maybe with diping into Thief?