Cheapest priced copy (The List): $0.35 at Card Kingdom, near mint, their price list as of .
Dauthi Mindripper 
Creature — Dauthi Minion · 2/1 · Uncommon · Tempest · #125
Shadow (This creature can block or be blocked by only creatures with shadow.)
Whenever this creature attacks and isn't blocked, you may sacrifice it. If you do, defending player discards three cards.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $0.35 to $0.49 at Card Kingdom
4 rulings from Wizards of the Coast
- 15 April 2013An ability that triggers when something "attacks and isn't blocked" triggers in the declare blockers step after blockers are declared if (1) that creature is attacking and (2) no creatures are declared to block it. It will trigger even if that creature was put onto the battlefield attacking rather than having been declared as an attacker in the declare attackers step.
- 19 March 2021Once a creature has been blocked, that creature remains blocked and will deal and be dealt combat damage even if it gains or loses shadow or if the blocking creature gains or loses shadow.
- 19 March 2021Multiple instances of shadow on the same creature are redundant.
- 19 March 2021If an attacking creature has multiple evasion abilities, such as shadow and flying, a creature can block it only if that creature satisfies all of the appropriate evasion abilities.