Everyone's done it, and it sucks. That having been said, I came up with a pretty good system that was netting me about 1 victory every four seconds.
Basically, make a deck consisting of Malort as the commander, and 1 Blood Grunt. Look for an empty deck in arena that has Elena as the commander, and put it on Auto. Each fight will last 1 round, and you won't have to wait for other cards to come out.
It works pretty well against empty Hydraulis decks, as well as the other ones that don't weaken or have strike. But because Elena has nothing to rally, you don't have to wait that extra fraction of a second while she does her thing (unlike Hydraulis, who tries to mimic the blood grunt).
Note that you can use a combination of any 1-drop card with 3 attack (hunter, black ops, artemis tank, or blood grunt) with a commander to rally it.
After that, all you have to do is click "fight" and "ok" until your eyes bleed.
