The problem is not bug. The effect is “sent from the hand” which is different than “discard” same as Soulkius.
i dont think this card works at the moment. if u use that other fabled card ( ive tried a few other cards) that discards cards from your hand and u do it while he's on board it doesnt let u tribute summon the monster u discarded. konomi fix this plx
Unlike most of the Fabled monsters, this thing's effect is an optional "when" effect, so it can miss its timing. (Not sure why they opted to do this when Dyf is one of the weakest Fableds in the first place, but eh.) The discard has to be the last thing to happen, so you'd need a card like Dark World Dealings to use it.