Bygone Bishop
Creature — Spirit Cleric
Flying
Whenever you cast a creature spell with mana value 3 or less, investigate. (Create a Clue token. It's an artifact with ", Sacrifice this artifact: Draw a card.")
Illustrated by
Commander Legends: Battle for Baldur's Gate#689RareEnglishLegality
Rulings
Casting a spell for an alternative cost, such as a madness cost, doesn’t change its mana value. For example, casting Twins of Maurer Estate (a card with mana cost 
and madness cost ) for its madness cost will not cause Bygone Bishop’s ability to trigger.
The token is named Clue and has the artifact subtype Clue. Clue isn’t a creature type.
The tokens are normal artifacts. For example, they can be sacrificed to cast Angelic Purge or targeted by Root Out.
If you sacrifice a Clue for another card’s cost or effect, such as that of Angelic Purge or Tamiyo’s Journal, you can’t also pay and sacrifice it to draw a card.