Efficiency can be determined simply by the reward you receive at certain mana costs (Counterspell and Cancel do the same thing, but Counterspell costs less), the total payoff you receive from a single card (Hull Breach and Decimate are both good cards, but Decimate usually covers much more ground), or the payoff you receive in conjunction with other cards (Anointed Procession makes other token production cards completely absurd if unchecked, which is usually better than adding one more card that simply makes tokens like Spectral Procession in a token strategy)
Behind every successful title is captivating gameplay, and card games aren't any different
Loki, the Deceiver is a mythic four mana 4/4 who, whenever he attacks, makes a tapped and attacking token copy of another Villain you control
Whenever one or more +1/+1 counters are put on Dreamdrinker Vampire, it gains menace until end of turn
Expect to find major issues around the edges or corners and some obvious surface imperfections, but no major creases
This reprint should make plenty of people happy