Booster packs aren't always the best way to get the best cards. I didn't do good with that. Instead I just got myself an untamed card through the market place that I see fit to purchase.
In regards the Gelatinous Cube. The thing that I find is that it can only be used for higher mana teams and you pretty much darn know your cards well enough in arrangement to know you have a winning team; otherwise it pretty much won't help buffering sneak attacks from the back.
RE: Splinterlands Strategy Session, Part 1 - The Gelatinous Cube