These cards seem well-balanced, but there are one or two touch-ups I'd recommend: For Atem, the correct OCG would be something like: Once per turn
Impact Tremors Enchantment Whenever a creature you control enters, this deals 1 damage to each opponent
You can typically pay one mana to trade a card for their best card in hand, or three mana to trade one card for their two worst cards
Still, if youre looking for great cards from 2025 and before, there are some great price drops to be had at TCGplayer to see in the new year, as well as some climbers across great cards
With other complementary artifact mana sources like Thran Dynamo and Grim Monolith, decks could count on being able to get the kind of mana you'd need to justify packing the cards that would let you use the mana from Metalworker to deliver the knockout blow, and their presence lets you turn that Metalworker mana into permanent giant amounts of mana rather than just a one shot deal
The layers of strategy, guesswork, and reading the other players come to the fore, as there are significant upsides for not getting any votes