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Yes, making proxies is legal, so long as you don't try to sell them
Sure, they might be able to put them back into a players hand from the battlefield or turn them into Islands, but mono-blue card effects just didnt let you search your deck for them, let alone place them on the battlefield
Thanks to affinity for artifacts, it often costs less than 4 mana, especially in lists packed with cheap artifacts like Ichor Wellspring or Chromatic Star
Kethek, Crucible Goliath Kethek, Crucible Goliath offers a fun type of sacrifice commander that can also help you take out your opponents creatures