At four mana, the best use for Razor Pendulum is discarding to Masticore (a fellow four-drop artifact) or sacrificing to Krark-Clan Ironworks (hey look, more four-drops!)
This is exactly the type of product we offer at Cards N Packs
It's presented as a boardgame style self-contained format that you play (given that it comes with play pieces and I'm pretty sure that none of the cards are tournament legal), but it's so expensive that I wouldn't be surprised if 99% of the copies bought are never actually played with or even opened and are just bought for collection
Goblin Bombardment is largely played in Commander, but its actually been on the rise in Modern recently, too
For collectors targeting specific cards, singles are almost always more cost-effective
Being a legendary is going to hold it back since for large creatures without evasion to win you need multiple in play to threaten lethal