Leagues are separate game economies from taoaxue's blog

"Protection while casting" support gem: Puts a temporary additional Energy Shield on the caster for the duration of the linked spell's cast time. This is very useful for skills such as Ice Nova where the player is generally in the middle of a group of monsters. It's also useful for use with the "Multiple Casts" support gem where the player spends longer than normal casting a sequence of spells.

PCG: When we were talking with Blizzard about Diablo III, they made the interesting remark that they're not altering any of the PvE balance of their classes to POE currency trade  make PvP more fair—they don't want to turn Diablo into a hypercompetitive e-sport, to paraphrase Blizzard. Not that there's one right way of doing things, of course—but with the addition of different leagues mentioned in the press release, how much of a focus or concern is PvP balance for Grinding Gear? 

Wilson: Leagues are separate game economies within one realm. They can have additional rulesets that modify gameplay. For example, in a cutthroat league, players drop all their items when they die. Some leagues are short-lived and offer opportunities for players who want to compete at levelling quickly. For example, an attrition league could last over a weekend, and would eliminate players periodically (based on who has the lowest experience) until only one remains. There's a much more detailed explanation of leagues here .

There are specific active skills, passive skills and support gems designed with PvP in mind. It's likely that dedicated PvP players will create specific PvP characters that have taken into account appropriate meta-game concerns. The items that are found in PvE (or awarded in PvP) are usable in both modes, and although they may be better suited to one style of play, there aren't many stats that are only useful in PvP or PvE alone buy POE currency .