Simple RAW for 5e V: The Disadvantage Strikes Back

[Mr Adventurer]

Re 151: Fire Giant Dreadnoughts (Volo's Guide to Monsters) can benefit from two shields, but that appears to be entirely unique to them. They also take a dex penalty in heavy armor? Who wrote that?

Their AC also only seems to give them +3 for doing so (they have plate mail, two shields, and AC 21).

It's not clear whether this is supposed to be from their -1 Dex modifier, or not.