2010 - AnimeVegas
It's pretty terrible, but I threw it together in a few hours, because a friend wanted me to go with her Pikachu...and then she didn't end up going

Vest thing - really shitty shiny velvet stuff...brown stripes glued onto the back
Tail whip - black rope and a craft foam lightening bolt
Ears - craft foam glued to large headphones...because electricity? I don't know...
Thunderstone necklace - green plastic chunk and transparent yellow glass paint