Okay, I was battling this really stupid guy named and
he had a erika's dratini out and a kangaskan and
slowpoke on his bench. I had a promo mewtwo out and I
attached a pluspower to mewtwo and I psyburned, he
said that it would only do ten damage, but if you read
the card, at the end it says: any other effects of an
attack still happen, i am quite sure that pluspower
would count as an effect so it should do twenty,
please verify this for me.

Thanks,

Will

Yes.  Any other NON-DAMAGING effects will happen.  This means that you could confuse, poison, etc. the Dratini.  PlusPower is a damaging effect, and this is affected by Strange Behavior.  And in the future, you might want to get a ruling before calling someone else stupid.  Besides, calling someone stupid isn’t very nice anyway.

Scott