Confidence:StrongSolidPlausibleTentativeSpeculative

• Najeela, the Blade-Blossom

  2R

  Legendary Creature — Human WarriorBGRUW

  Damage pair: both cards convert effects into damage. They stack in a damage-heavy deck; on their own they're a value engine, not a closed loop.
• Archivist of Gondor

  2U

  Creature — Human AdvisorU

  Both cards trigger on damage dealt — they fire together.
• Sygg, Wanderwine Wisdom // Sygg, Wanderbrine Shield

  1U

  Legendary Creature — Merfolk Wizard // Legendary Creature — Merfolk RogueUW

  Both cards trigger on damage dealt — they fire together.
• Reanimate

  B

  SorceryB

  Reanimate puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Helping Hand

  W

  SorceryW

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

  B

  SorceryB

  Unearth puts Kosei, Penitent Warlord 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 Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• The Beast, Deathless Prince

  2BR

  Legendary Creature — DemonBR

  Both cards trigger on damage dealt — they fire together.
• Can't Stay Away

  WB

  SorceryBW

  Can't Stay Away puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Vraska the Unseen

  3BG

  Legendary Planeswalker — VraskaBG

  Both cards trigger on damage dealt — they fire together.
• Priest of Fell Rites

  WB

  Creature — Human WarlockBW

  Priest of Fell Rites puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• The Rani

  1UBR

  Legendary Creature — Time Lord ScientistBRU

  Both cards trigger on damage dealt — they fire together.
• One with Nature

  G

  Enchantment — AuraG

  Both cards trigger on damage dealt — they fire together.
• Resistance Is Futile

  1B

  SorceryB

  Resistance Is Futile puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Gonti, Night Minister

  2BB

  Legendary Creature — Aetherborn RogueB

  Both cards trigger on damage dealt — they fire together.
• Lost Jitte

  1

  Legendary Artifact — EquipmentC

  Both cards trigger on damage dealt — they fire together.
• Animate Dead

  1B

  Enchantment — AuraB

  Animate Dead puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Exhume

  1B

  SorceryB

  Exhume puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Return Triumphant

  1W

  SorceryW

  Return Triumphant puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Felix Five-Boots

  2BGU

  Legendary Creature — Ooze RogueBGU

  Felix Five-Boots makes Kosei, Penitent Warlord's triggered ability trigger an additional time — each time it fires, you get it twice. Value, not a loop.
• Life // Death

  G1B

  Sorcery // SorceryBG

  Life puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.
• Puppet Master, String Puller

  2R

  Legendary Creature — Human Artificer VillainR

  Both cards trigger on damage dealt — they fire together.
• Teysa, Envoy of Ghosts

  5WB

  Legendary Creature — Human AdvisorBW

  Both cards trigger on damage dealt — they fire together.
• Godo, Bandit Warlord

  5R

  Legendary Creature — Human BarbarianR

  Godo, Bandit Warlord grants an extra combat phase, enabling Kosei, Penitent Warlord's combat-trigger payoff.
• Dance of the Dead

  1B

  Enchantment — AuraB

  Dance of the Dead puts Kosei, Penitent Warlord onto the battlefield from a graveyard without casting it, so its mana cost is never paid.