DiabloFans

Other stuff aside, I'd like to point out the obvious and say that the build you linked isn't quite the one you're describing.

1. put down hydra first
2. start spamming mines
3. watch the hydra heads disappear one by one when you reach around 4 mines

It seems like there's a limit where you can't place down more than 6 of anything. Notice that If you put down 7 mines, the first one will disappear to maintain a total of 6. I would expect that to be intended rather than a bug (otherwise you could set down 300 mines down before pulling each room and effectiveley 1 shot anything).
Hydra heads seem to each count as 1 item towards this limit. I'm not sure if that part is intended.

I would have to agree with fhnhf. I'm sure there's a small handful of people out there that think they can get away with playing on a laptop touchpad