The tips are completely wrong. Copycat DIDN'T GAIN the original stat of the selected monster, but its stat BECOMES EQUAL to the selected monster's stat. So if you using Yami, e.g : copycat att = 200 --> select BEWD (3000 original att) --> your Copycat becomes equal to BEWD original att (3000) with yami on the field, if yami leaves the field, your copycat att becomes 2800. I have seen it so many times since Pegasus uses it during his event. So it's better to not use power of dark skill when u decide to use this card
This card is especially good with power of dark. Just like golden apples, it would not only match their attack, but exceed it by 200. Also works well with wonder ballons/pumprincess since it copies original attack.