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You also need to watch if your creatures have taken lethal damage and an opponent can remove Darksteel Forge from the battlefield, either exiling it or putting it back in your hand, which will cause all your creatures to die to state-based actions
Always cross-check completed sales on TCGplayer and eBay not just list prices, which can run 2 to 3 times above a card's actual market value
Skullclamp is a staple of Token decks, as most are going to be 1/1s, allowing you to easily draw out a lot of cards from your deck to get to your win conditions
You might well have seen one or two of these creatures in the past and not realized that theyre usually part of a cycle, with one in each color
Id wait until about a week or two after the set drops (when supply is the highest) and then trade for as many of these as you can