(http://i.imgur.com/aLCzXDP.png)
That's how you do it, simple as that.
If you want you could bring another spell but I've never tried using any other spell/staff there, you want to keep blood barraging cause it heals and that's the point so there is no need to change spell.
Focus on dragging the boss next to minion(s) and attack one of em, I'd suggest attacking boss until you got more than 75HP and then start killing minion(s), It'll take more runes but will save you food and in my opinion that is why you go there using magic, you want the trip to last long.
Feel free to message me in-game if you got more questions. :)