Similar to the ruling below, the attack is not affected (does full damage). Its the result that gets amended:
Q. Let's say Charizard-EX uses "Burn Down" on a Jumpluff. Would Jumpluff get to use it's "Buffer" or not (because "Burn Down" is not affected by Poke-Bodies)?
A. The Burn Down attack is not affected because Buffer does not kick in until *after* Burn Down has done all its damage. However, after Burn Down has done its mega damage, Buffer kicks in and if successful would get to remove damage counters from Jumpluff until 10 HP are left. (Feb 17, 2005 PUI Rules Team)