Matrix, every duplicate will fight you. In Wikidata you may kill of every duplicate. This is done by merging them. The result is good; statements are combined, articles are combined in the oldest item of the two.
Merging is easiest using the merge gadget. There are loads of duplicates, there could not be as much as 20% doubles .
A first tool to attack this multitude is the "Wikidata duplicate item finder". Based on the assumption that everything has an unique name you will get a list with many possible doubles. With this tool Magnus very much provides a first tool to fight the agent Smiths of Wikidata. Other tools are needed; for instance to look for a combination of labels and date of birth.