Slither Blade Variants Slither Blade is one of the first creatures that comes to mind when I think of unblockable which dates my return to Magic since there are variants of the card that predate Amonkhet like Triton Shorestalker and Gudul Lurker
Exploring the "return to hand" thematic and giving it the "Level 5 or higher" requirement

Symbiotic Swarm Deck List Commander (1) 1 Kathril, Aspect Warper Planeswalkers (1) 1 Ajani Unyielding Creatures (34) 1 Tayam, Luminous Enigma 1 Nikara, Lair Scavenger 1 Yannik, Scavenging Sentinel 1 Avenging Huntbonder 1 Cartographers Hawk 1 Vitality Hunter 1 Daring Fiendbonder 1 Slippery Bogbonder 1 Void Beckoner 1 Titanoth Rex 1 Akroma, Angel of Wrath 1 Angel of Finality 1 Cataclysmic Gearhulk 1 Kalemnes Captain 1 Odric, Lunarch Marshal 1 Reveillark 1 Solemn Recruit 1 Sunblast Angel 1 Zetalpa, Primal Dawn 1 Cairn Wanderer 1 Soul of Innistrad 1 Soulflayer 1 Hornet Queen 1 Majestic Myriarch 1 Splinterfright 1 Archon of Valors Reach 1 Karametra, God of Harvests 1 Aerial Responder 1 Vampire Nighthawk 1 Acidic Slime 1 Sakura-Tribe Elder 1 Satyr Wayfinder 1 Skullwinder 1 Nyx Weaver Spells (13) 1 Blood Curdle 1 Unbreakable Bond 1 Obscuring Haze 1 Selective Adaptation 1 Ever After 1 Duneblast 1 Unburial Rites 1 3Deathsprout 1 Despark 1 Grisly Salvage Artifacts (7) 1 Bonders Ornament 1 Netherborn Altar 1 Mimic Vat 1 Arcane Signet 1 Commanders Sphere 1 Sol Ring 1 Swiftfoot Boots Enchantments (6) 1 Martial Impetus 1 Parasitic Impetus 1 Predatory Impetus 1 Together Forever 1 Abzan Ascendancy 1 Deadbridge Chant Lands (38) 1 Nesting Grounds 1 Canopy Vista 1 Caves of Koilos 1 Exotic Orchard 1 Gavony Township 1 Grim Backwoods 1 Sungrass Prairie 1 Blighted Woodland 1 Command Tower 1 Golgari Rot Farm 1 Krosan Verge 1 Memorial to Folly 1 Myriad Landscape 1 Orzhov Basilica 1 Sandsteppe Citadel 1 Selesnya Sanctuary 1 Blossoming Sands 1 Evolving Wilds 1 Jungle Hollow 1 Scoured Barrens 7 Plains 7 Swamp 4 Forest

Either way, you'll be thrilled to pick up either one while drafting
If a card is a 1:1 or near enough remake of a card that does exist, then I am against it and so should everyone else
It boils down to three key factors: Limited Supply : The rarity and cap on card production make them scarce commodities over time