Unexpected Windfall is an okay card to play in treasure decks, or as a way to discard and draw, but nothing more
I used to joke that every single sideboard I played had at least one Needle in it when I started playing Legacy
It even shares the mana value of Gravedigger, so I get why this card costs this much, even if I would never build around it
After years of swearing that they wouldn't make mechanically unique promos, going back to the disastrous release of the Nalathni Dragon promo in the early '90s, Wizards somehow forgot this lesson and declared that they were once again going to make mechanically unique promos
But add that your creatures can help cast Lethal Scheme by convoking and you get a free kill spell, up to four loot triggers, +1/+1 counters, and anything in between at best
Trigger Happy This two-cost uncommon Red instant will copy a triggered ability of any target permanent and you control it