Purple patch is a colloquial term for a pre-Issue 1 update in which the developers increased the difficulty of enemies higher-level than the player. "Purple" refers to the Con System in the game where enemies four or more con levels will have their name appear as purple in the target window. Before the patch was implemented, full groups of heroes were often able to defeat enemies that were ten levels higher than them.
Indirectly, the purple patch reduced the potential teaming pool. Prior to the patch, a character was still reasonably effective against enemies 5 levels higher, and that character could team with characters +/-5 levels above or below him or her. Post-purple patch, characters were practically limited to fighting enemies 2 to 3 levels above them, with 4 being the absolute practical cap.
When contemporary forum-goers talk about the "purple patch", they may be referring to the way player character effectiveness scales against different-level enemies. To use the table below, multiply the effects of your powers by the value in the Above column if you are Level levels above your target, or by the value in the Below column if you are Level levels below your target.
Main article: Attack Mechanics
A character's chance to hit is not directly affected by the combat modifiers, above. While Defense debuffs applied to the target affect chance to hit and are subject to the purple patch, and ToHit debuffs applied to the player affect chance to hit and are also subject to the purple patch, a character's base hit chance follows a different formula.