Nothing too severe. Mixed up two Pokemon quite a bit in a recent playthrough (Clothes the Noctowl and Blanket the Articuno). Could have been the random name, partially. Likely had the same sprite, on top of being similar materials (depending on whether you see it as a blanket of snow or not, anyways).
Occasionally forgets to teach a TM move for a gym or something. Almost Wonder Traded away a shiny once, in Generation 6. Hit the Power button before it went through.
Oh, and most of that first Nuzlocke run. Lost at least one Pokemon while training. Went in underleveled slightly sometimes. Tried to save one Pokemon, which cost way more than one death.