Opposite to traditional magic items

POV: a DM and Player of Artifiser.

I have thought up the idea that some magic items could have equal counterparts such as the "immovable rod" has the counter of the "unstoppable Disc". 

I am one asking about balancing the item mentioned above bit also any other items that you believe would have one/ what they maybe.

A “Continual Shadow” could counter Continual Flame on items, if you are home brewing.

Just RAW, resistance on armor and the like counters corresponding elemental damage.  Which is one of the things a mid -level Artificer can do via infusion.