I got into Hackmons Cup recently. This battle embodies the glorious insanity of the mode. I had an ordinary start and was on the back foot for most of the battle. Ended up 1 v 3 at the end, with the 1 being my Giga Drain/Bubble Cyndaquil. Since it had Shell Smash, in the back of my mind I thought it could possibly sweep, but didn't think it was likely. But I soon realized it was my only chance, so saved it and then set up when I had the chance. I think I overestimated Combee in my mind, Bubble was an easy 2HKO despite pitiful BP and no STAB. Cleffa got off a Mud Slap which made for an even nervier finish against their Ttar. Right on cue the first Giga Drain missed, and I was chopped down to red health. 2nd hit, and took me back to half health, which was just enough to survive the second attack on 4% HP.
They really should have taken better care of their Wonder Guard mon. The only thing I had for it was Astonish, and I was just hoping they would sac it before KO'ing my Tyrantrum. Of course there's no way to know all this for sure, but as a general rule it's a good idea to save a Wonder Guard mon in this mode along with other potential win cons. If you take out the one thing you know can damage it, then they may not have anything else as was the case here.
http://replay.pokemonshowdown.com/hackmonscup-341881079