When it dies you have two options, place two +1/+1 counters on your stuff, or dig 7, can drop up to 4 mana value of nonlands onto the battlefield ready to go
Even a card like Advent of the Wurm has multiple uses, either as a surprise blocker or big attacker
This Alternate Art promo bucks the trend of valuable promo cards hailing from real-world competitions
The grammar change ("you" to "your opponent" and "your" to "your opponent's") definitely helps, and the cost helps keep this card in check (although, honestly, discarding a card is a fair enough cost - I don't support the whole match-type part of this, seeing as this is already a situational card)
The cards narrative, when combined with the detailed imagery, makes it one of its sets biggest hits