Been playing Concealment since launch, so a few of these things might sound familiar. Anyways, here's my two cents for what it's worth.
Concealment
2 Piece: Increases energy reserves by 5.
4 Piece: Shiv/Veiled strike grants 5-10% bonus to alacrity for 5s after use.
6 Piece: When used from stealth backstab critically hits the target (Cannot occur more than once per minute).