(He allows you to tap your equipment for mana!) Theoretical Duplication I just don't think copying your opponent's creatures for the turn (or more likely creature, singular) is that strong
Add cards to your deck as you normally would until you've completed building your deck
Gollum, Patient Plotter Gollum, Patient Plotter gives you a repeatable method for being tempted by The Ring, and can help you avoid commander tax
Some of that is just good fortune in how all these effects are worded, but Id say its more that discarding is an inherently effective way to interface with Magic s core mechanics
The theming lends a sort of annoying inconsistency to your decks and the board state that might be funny at first glance but becomes rather grating over time
It also carries a significant power boost ability that can come in real handy in a pinch, hence why its a desirable level three card