The green ability helped you answer artifacts and enchantments, while the blue ability helped you deal with creatures
Cheating on mana is typically a great way to win games, and Kellan can help you do just that

Abyssal Harvester Abzan Charm Acrobatic Maneuver Ajani Fells the Godsire Ajani Unyielding Ajani, Inspiring Leader Alabaster Host Intercessor Angel of Deliverance Angelic Ascension Angelic Edict Anoint with Affliction Archenemy's Charm Astarion's Thirst Astral Confrontation Astral Drift Astral Slide Auron, Venerated Guardian Baffling End Baleful Mastery Banish from Edoras Banisher Priest Become Anonymous Bind (playtest) Bishop of Binding Blade Banish Blazing Hope Blessed Light Blessed Reincarnation Blur Bogslither's Embrace Boneclad Necromancer Bring to Trial Brittle Effigy Brutal Cathar Calix, Destiny's Hand Carrion Imp Catapult Master Cemetery Reaper Chained to the Rocks Circle of Confinement Citizen's Arrest Cloudshift Cold Storage Colossal Whale Complete Disregard Conjurer's Closet Constricting Sliver Consuming Ashes Contraband Livestock Crack in Time Crib Swap Cruel Alliance Dakkon, Shadow Slayer Dark Impostor Daydream Deadly Rollick Death in the Family Death-Mask Duplicant Deathrite Shaman Declaration in Stone Devout Decree Dimensional Exile Dimir Doppelganger Dino DNA Dire Tactics Driftgloom Coyote Early Winter Eat to Extinction Eaten Alive Eater of the Dead Emeritus of Truce Endless Sands

Myr Retriever can pull off all the same combos as Marvin, Murderous Mimic , but it takes a little longer to set up
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Cyberdrive Awakener is a six-mana Construct who gives my artifact creatures flying and will turn my noncreature artifacts into 4/4 artifact creatures until end of turn