For example, in a previous A20 run I had I took Metallicize as Ironclad late in Act 1 because I was facing the Guardian and I didn't encounter other good block plans. Prior to that, I tended to avoid Metallicize to save spots for other block cards instead as it was too slow. This situation made me realize that having a Metallicize in your deck isn't that bad, especially if you need block NOW and you can counteract having it in your deck later on with draw/exhaust.