Rogue talent · row 2 of Subtlety, from level 15 (10 with Talented 5/5) · Physical

Dirty Tricks

Reduces the Energy cost of your Sap and Blind abilities by 25/50%.

Game files · build 1.60.1.70291New in ForeverRead from the WoW Forever beta client, build 1.60.1.70291.

In Blizzard's notes

What Blizzard said about Dirty Tricks, each line checked against the files.

Matches the files
Dirty Tricks: Formerly Improved Sap. Moved from row 4 up to row 2. (Redesigned.) Sap never breaks Stealth now baseline. Instead, this talent reduces the Energy cost of Sap and Blind by a substantial amount.
The files Dirty Tricks (1224782) is Subtlety row 2 and cuts Sap and Blind Energy costs by 25/50% (Sap 65, Blind 30). Improved Sap, Classic's row 4 talent with a 30% chance to restealth, is gone, and Sap's tooltip says 'Does not break Stealth.'
Dirty Tricks Sap Blind Class deep dives: Rogue and Warlock

69876 Sep 16First beta build we archived. No changes in the client files since.