I had considered either Hurkyl's Recall or Rebuild in the past as a blue answer to the artifact deck, however I deemed them to be too hateful for my cube. There are also cards like Annul or Steel Sabotage, though these seem a bit too low-impact. Not really sure of what all the options available are, but does anyone run artifact answers in blue?
I haven't always felt this way, but I feel like letting each color do what it does well is the best way to approach this. Unfortunately, that means blue lacks removal (outside counters and maybe some bounce). Blue does so many things well. Does it really also need answers to artifacts? That's sort of what splashing is about. If you build a deck and it might struggle with artifacts, well maybe you need to factor in a white/red/green splash to deal with artifacts? Again, I haven't always been in favor of this design - I went through a phase of trying to jam removal in each color (even bad removal). Now I just think this makes the color pie more meaningful and adds additional dimension to drafting.
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http://riptidelab.com/forum/threads/modular-cube-5-colors.800/
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