Especially with a difficult casting cost tacked onto it
There's no learning curve, no tutorials to sit through, and no design files to manage
Cards that require you to descend every turn or so are also good payoffs, like Corpses of the Lost
Unified Minds is one of the best sets of the Sun & Moon generation, and features valuable Tag Team cards that have risen in price
Alongside this striking artwork of the first-ever rare Dragon in Magics history, this Secret Lair (Secret Lair 295) also featured some other notable cards from Alpha, including Swords to Plowshares, Giant Growth and others
This is more of a suggestion than a rule, as some archetypes, usually the anime ones (say Blackwings or Performapals) do not have a central mechanic, but especially in customs, where it is almost guaranteed that the opponent is seeing your cards for the first time, it is imperative that it is clear how the deck works