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So with how I understand layers, auras will always give chromium the stat buffs since they're applied in layer 7c, while his "become a 1/1" happens beforehand in layer 7b. But ability adding/removal all happens in the same layer. Thus the effects are done in timestamp order.
What does that mean? You need to apply auras after using chromium's ability for them to give him any card text like vigilance, lifelink, etc. And if you use it a second time, currently applied auras will be wiped since they have an older timestamp.
This might not matter too much as a hexproof unblockable 21/21 will still get the job done, but it's a detail I think it could be easy to miss.