Deathly Ride bug
I cast Deathly Ride targeting the Tenacious Tomeseeker in my graveyard. Because I had Chancellor of Tales in play, it let me double the adventure spell, but the Tomeseeker was the only creature in my graveyard, so I targeted it twice. When the Deathly Ride resolved, Fell Horseman went to my graveyard rather than the exile zone (on an adventure). I thought this might be because the second Deathly Ride fizzled after Tomeseeker was no longer in my graveyard, but I had done this exact sequence previously, except targeting Spellsworn Coven rather than Tenacious Tomeseeker, and the Fell Horseman went to my exile (adventure) zone as expected.
This bug led to my third loss in a sealed event, so I am requesting a refund of my entry fee.