I mastered my grenades at Darkhart, and mastered my staff at Timothy. I would have mastered it at Darkhart as well, but there was someone there and I wanted to level alone. If you use the bug at Darkhart where he doesn't attack you and keeps his distance, staff and grenades won't be too hard to master. There's also quite a useful bug with grenades that, if you keep clicking the mouse button and mashing all the hotkeys for the grenade ammos, they'll be thrown about ten times quicker than without the bug.
Hope that helps.