Reanimation effects can bring back beaters like Sheloldred, Whispering One, Jin-Gitaxias, Core Augur, and Toxrill, the Corrosive
Tomer shows you how to turn the Merfolk precon into an unstoppable powerhouse with either Hakbal or Kumena at the helm
Then, you want to include just enough tribal cards of your type so that they can synergize without overcrowding

Sliver Overlord Sliver Overlord | Illustration by Tony Szczudlo Commander (1) Creature (31) Homing Sliver Necrotic Sliver Lavabelly Sliver Basal Sliver Gemhide Sliver Sentinel Sliver Amoeboid Changeling Sedge Sliver Harmonic Sliver Crypt Sliver Heart Sliver Diffusion Sliver Cloudshredder Sliver Manaweft Sliver Ignoble Hierarch Hibernation Sliver Shifting Sliver Root Sliver Crystalline Sliver Bonescythe Sliver Galerider Sliver Bloom Tender Birds of Paradise Sliver Hivelord The First Sliver Morophon, the Boundless Sliver Legion Sliver Queen Sliver Gravemother Hatchery Sliver Chomping Changeling Instant (14) Brainstorm Delay Swords to Plowshares Assassin's Trophy Veil of Summer Eladamri's Call Flusterstorm Cyclonic Rift Worldly Tutor Mana Drain Vampiric Tutor Deflecting Swat Enlightened Tutor Fierce Guardianship Sorcery (4) Kodama's Reach Farseek Eldritch Evolution Demonic Tutor Enchantment (8) Rhythm of the Wild Utopia Sprawl Cryptolith Rite Carpet of Flowers Mana Echoes Training Grounds Rhystic Study Sylvan Library Artifact (9) Arcane Signet Sol Ring Fellwar Stone Chromatic Lantern Door of Destinies Coat of Arms Urza's Incubator Chrome Mox Thrumming Hivepool Land (33) Island Mountain Swamp Plains Forest Command Tower Unclaimed Territory Yavimaya, Cradle of Growth Stomping Ground Marsh Flats Hallowed Fountain Godless Shrine Temple Garden Overgrown Tomb Arid Mesa Watery Grave Verdant Catacombs Steam Vents Sacred Foundry City of Brass Blood Crypt Misty Rainforest Breeding Pool Windswept Heath Scalding Tarn Mana Confluence Urborg, Tomb of Yawgmoth Wooded Foothills Flooded Strand Bloodstained Mire Polluted Delta Cavern of Souls Sliver Hive Slivers have been around in Magic since, well, almost forever

They are definitely good
Sure, the Avengers Plant tokens get bigger with time, but this cards Beasts are more relevant if the actual creature dies quickly