Whenever Gollum attacks, look at the top two cards of your library, put them back in any order, then choose land or nonland. An opponent guesses whether the top card of your library is the chosen kind. Reveal that card. If they guessed right, remove Gollum from combat. Otherwise, you draw a card and Gollum can't be blocked this turn.
Gollum is a cheap, evasive black commander that reliably draws you a card and goes unblockable every combat once you set up the top of your library. Suit him up with cheap evasion and pump to deal commander damage, or just grind value with the repeatable card draw while a sacrifice/drain engine does the killing. The early game is about getting Gollum online turn 2-3 and protecting him so the attack triggers stay flowing.
Two-mana commander that comes down fast and rebuilds cheaply after removal.
You control the top of your library, so you almost always win the guess for an extra card and unblockable Gollum.
Built-in card advantage in mono-black, which can otherwise struggle to refill.
Reliable evasion makes him a strong Voltron/commander-damage carrier.
Low base power means he does little without equipment, auras, or pump.
Mono-black has limited interaction with artifacts and enchantments.
A savvy opponent can occasionally guess right and pull him out of combat, blunting the engine.
Spot removal and board wipes set you back even if the recast cost is low.
Lets you attack, trigger Gollum, then pull him back to dodge any blocker or guess.
Add efficient mana rocks and tutors (Demonic Tutor, Vampiric Tutor) to find your equipment and protection faster, and lean into low-cost evasion pieces so every swing draws cards. Include strong protection (Lightning Greaves, Swiftfoot Boots) and a finisher like Torment of Hailfire or Exsanguinate so your card advantage converts to a win. Tighten the curve and add black's premium removal so you can keep Gollum attacking unimpeded each turn.