In a recent video I made describing how the KCI infinite combo works, I stated that mana abilities could be activated while casting Mox Opal, a spell that costs 0 mana. A commentor contended that this was not accurate because players can only activate mana abilities if a spell asks for a “mana payment” . I replied that a payment of 0 mana should still count as a mana payment, citing CR 117.5 as my rationale for these costs being handled the same way. In looking into it further, I've run across a number of confusing and conflicting opinions from some pretty heavy hitters rules-wise. So I'd like an fficial answer on this so I'll know once and for all. Does casting a spell whose mana cost is 0 allow you to activate mana abilities or not?

Hi,

One of the steps of casting a spell is:

601.2g If the total cost includes a mana payment, the player then has a chance to activate mana abilities (see rule 605, “Mana Abilities”). Mana abilities must be activated before costs are paid.

{0} is a cost, but it's not a cost that requires mana. There's no mana payment included when you're you casting Mox Opal, so you skip 601.2g and thus you don't get the opportunity to activate mana abilities (like the Ironwork's ability).

Thanks,
Nathan Long
Magic Rules NetRep