You don't understand the combo. I have on the battlefield, for instance, 5 islands, 2 myr galvanizers and four iron myrs. I cast blue sun zenith, paying 5 (we are currently at X = 3). Then I tap three iron myrs (adding 3 to X). Then I pay one using the last iron myr, tap one of the galvanizers, which lets me untap each other myr I control. Then I tap 3 iron myrs, adding 3 more to X, tap one more iron myr and the other, untapped, myr galvanizer and untap all other myrs I control. Do this for a while, BAM. Milled your opponents deck. Now, they could try to mana leak it, but you can just pay it using the same tactic. If the iron myrs were silver myrs (tap for blue) and they try to cancel your blue sun zenith, you can just mana leak it using the same tactic above.
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Well, the idea behind blue sun zenith is that /target/ player draws X cards, so in infinitely ramp into it, making them mill.