Magma Sliver is a rare Creature — Sliver card from Legions (LGN), collector number 107. Current market price: $7.52 (foil $49.99), TCGplayer market prices via Scryfall.
All Slivers have "{T}: Target Sliver creature gets +X/+0 until end of turn, where X is the number of Slivers on the battlefield."