Confidence:StrongSolidPlausibleTentativeSpeculative

• Helping Hand

  W

  SorceryW

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

  B

  SorceryB

  Unearth puts Skystreak Engineer onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Reanimate

  B

  SorceryB

  Reanimate puts Skystreak Engineer onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Fiery Gambit

  2R

  SorceryR

  Fiery Gambit untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Grave Researcher // Reanimate

  2BB

  Creature — Troll Warlock // SorceryB

  Grave Researcher puts Skystreak Engineer onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Innocuous Researcher

  3G

  Creature — Centaur DetectiveG

  Innocuous Researcher untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Time Spiral

  4UU

  SorceryU

  Time Spiral untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Nissa, Vastwood Seer // Nissa, Sage Animist

  2G

  Legendary Creature — Elf Scout // Legendary Planeswalker — NissaG

  Nissa, Vastwood Seer untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Elrond, Moon-Reader

  2U

  Legendary Creature — Elf NobleU

  Skystreak Engineer has activated abilities that aren't mana abilities, fueling Elrond, Moon-Reader's activation-trigger.
• Rewind

  2UU

  InstantU

  Rewind untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Beledros Witherbloom

  5BG

  Legendary Creature — Elder DragonBG

  Beledros Witherbloom untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Finale of Revelation

  XUU

  SorceryU

  Finale of Revelation untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Prophet of Kruphix

  3GU

  Creature — Human WizardGU

  Prophet of Kruphix untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Bumi, Unleashed

  3RG

  Legendary Creature — Human Noble AllyGR

  Bumi, Unleashed untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Sphinx of the Second Sun

  6UU

  Creature — SphinxU

  Sphinx of the Second Sun untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Wilderness Reclamation

  3G

  EnchantmentG

  Wilderness Reclamation untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Sword of Feast and Famine

  3

  Artifact — EquipmentC

  Sword of Feast and Famine untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Treachery

  3UU

  Enchantment — AuraU

  Treachery untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Zacama, Primal Calamity

  6RGW

  Legendary Creature — Elder DinosaurGRW

  Zacama, Primal Calamity untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Llanowar Druid

  1G

  Creature — Elf DruidG

  Llanowar Druid untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Nissa, Worldwaker

  3GG

  Legendary Planeswalker — NissaG

  Nissa, Worldwaker untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Cyclonus, the Saboteur // Cyclonus, Cybertronian Fighter

  2UB

  Legendary Artifact Creature — Robot // Legendary Artifact — VehicleBU

  Cyclonus, the Saboteur untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Nature's Will

  2GG

  EnchantmentG

  Nature's Will untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Emrakul, the Exigent Doom

  10

  Legendary Creature — EldraziC

  Emrakul, the Exigent Doom untaps lands, fueling Skystreak Engineer's mana-hungry effect.
• Awakening

  2GG

  EnchantmentG

  Awakening untaps lands, fueling Skystreak Engineer's mana-hungry effect.