Tactic #1: Difficulty: Moderately Hard, Black to move (From a win against a GM online).
Tactic #2: Difficulty: Easy, White to move.
Tactic #3: Difficulty: Hard, Black to move (From a win against a different GM online).
Solutions:
#1:
1. ...Bc3! is the best way to simplify. (1. ...Bd1 is the only other reasonable move) 2. Nxg4 (Any rook move loses to either Bxf6 or taking the rook.) 2. ...Bxe5 3. Nxe5 Ke7 with a superior ending that was eventually converted.
#2:
1. c4! wins a pawn. 1. ...Qd8 2. cxd5 and if 2. ...Qxd5 3. Qxc5! keeps the pawn. In the game, black played 2. ...cxd4, when 3. Qxe4+! gained the pawn anyway, and white went on to quickly win.
#3:
Black is up a piece, but it is being attacked and is pinned to the rook.
1. ...Bxg2!! is the finishing blow. Black will remain up material with an easy win in sight. In the game, 2. Qxd4 Qxh3+ and white resigned due to losing the f1 rook after Kg1 Qh1+ Kf2 Bxf1.