@Sicaror I tried your method for a bit and didn't get anything really good. Getting the highest tier Diamond is really easy and the difference in what I craft using greens vs diamonds is significant
When upgrading the Rocket Launchers AOE past 30 it will start increasing it's DPS each upgrade even though it's damage value remains the same. The AOE upgrades prior to 30 weren't increasing the DPS with each upgrade so I think a bug is going on here
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It stacks additively. So if you have 98% armor pen from the upgrade, and 1.98% from rebirths, you have a total of 99.98% penetration.