Creature - Illusion 1/5, 3B (4) {B}: Phantasmal Fiend gets +1/-1 until end of turn. {1}{U}: Switch Phantasmal Fiend's power and toughness until end of turn.1
Illus. Scott Kirschner
As per Rule 418.5a, power and toughness switching is applied after any effects that modify power/toughness. This means that even if new spells and abilities are played to modify power/toughness, they are applied before the switch. [D'Angelo 2006/01/01]
Note - This card was of creature type "Phantasm" and not "Illusion" until Oracle 2006/07/14.