I think that question would be better for Adam to answer but is Nickel from II the same one from BFDI?

Since we don’t control Nickel on BFDIA/IDFB/BFB, we’re not one to speak for them. We can only speak for our Nickel. As a result, there is no concrete answer to whether or not the other one is our NIckel.

However, Adam has said that Nickel from the II series and Nickel from the BFDI series are technically the same character, but on two different timelines. This explains the difference in character - different environments. Though Adam has pointed out that BFDIA Nickel shares more similarities with II Nickel than BFB Nickel does.