Confidence:StrongSolidPlausibleTentativeSpeculative

• Reanimate

  B

  SorceryB

  Reanimate puts Heir to Dragonfire onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Helping Hand

  W

  SorceryW

  Helping Hand puts Heir to Dragonfire onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Unearth

  B

  SorceryB

  Unearth puts Heir to Dragonfire onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Grave Researcher // Reanimate

  2BB

  Creature — Troll Warlock // SorceryB

  Grave Researcher puts Heir to Dragonfire onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Elrond, Moon-Reader

  2U

  Legendary Creature — Elf NobleU

  Heir to Dragonfire has activated abilities that aren't mana abilities, fueling Elrond, Moon-Reader's activation-trigger.