Like most Magic: The Gathering cards, the value of Gollum, Obsessed Stalker depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Tales of Middle-earth Commander)
It needs to be built specifically around and is typically quite slow to yield returns despite being so cheap to cast itself
This build is happy to grind out the game by returning Poison Apples and Swords of Truth with Tamatoas ability
In artifact-heavy builds it might find Senseis Divining Top or Skullclamp
On the other hand, if your deck was made up entirely of weaker, one-mana spells, you wouldn't be making the best possible play on any turn beyond the first one
Gardevoir is primarily there to power up other Psychic-type Pokemon like Mewtwo ex