Some of the achievements for the miniset are truly obnoxious. I'm still waiting to decide whether the dh one or the paladin one are the actual worst. One needs opponents to do something, one needs complete randomness that has really low odds of happening. Truly a joy to behold.
I just finished the caravans one and it's, by far, the worst achievement so far. Oh my yogg was bad to be certain, but due to the sheer amount of exceedingly dumb individuals on ladder, having a caravan survive more than one turn is absurdly difficult. When I was doing it with shaman a sodding hunter had 4 choices to hit with the overkill spell: two 2/4 crabriders, the 1/3 give rush murloc and the caravan, while I had 7 cards in hand...he chose to hit the caravan. I don't try to even hit face (in the blind hope people realise that I don't care to win) but I was so pissed I buffed the board twice and killed him two turns later. Can't abide this level of stupidity.
So the best way to do that achievement in standard is hope you find AFK players...that's about it.
I want to point out also that the "play x number of cards that cost naturally 8 or more" is bugged since for some reason any combo with aviana (aviana + kun + maly + 2 UI etc) doesn't trigger it even though it obviously should.
You also don't need any luck for the rancor one, you can simply load your deck with 0 cost minions, rancor and draw and just play them out and rancor pretty early if you put enough card draw in your deck.
But speaking of bugged, I think the bulked up achievement is bugged too since it triggered when I had just 3 copies of the same minion, not 4.