Tomb Raider 2: The Dagger Of Xian

Level skip:
Press / to put a flare in Lara's hand. Have Lara walk one step forward (with [Shift]), one step back (with [Shift]), rotate in three full circles in any direction (with [Shift]), and jump forward (with [Alt]).

All weapons:
Press / to put a flare in Lara's hand. Have Lara walk one step forward (with [Shift]), one step back (with [Shift]), rotate in three full circles to the right (with [Shift]), and jump back (with [Alt]).

Exploding Lara:
Have Lara walk one step forward (with [Shift]), one step back (with [Shift]), rotate in three full circles to the right (with [Shift]), and jump back (with [Alt]).

Hint: Exiting Venice:

Give Lara's boat extra power after pulling the switch (right before the clock starts). This will allow it to travel up the long ramp that leads to some windows. Lara will crash through the windows and land in the canal just before the exit with plenty of time to spare.
Alternatively, swim under the mines and you will automatically start the next level with the boat. 
Alternatively, pull the switch, then swim under the door and climb back into the boat. The, go to the exit door without beating the clock. 
Hint: Treasure room:
There is a switch in between two statues in the hedge maze at Lara's house that will open a door to a treasure room. To reach the switch, use the following steps from the start of the hedge maze: Left, Right (when you reach an archway), Right, Left, Left, Left, Right, Right, Left, Left, Right, Right, Left, Right, Right, Left, Right, Left, Left, Left, Right. Enter the hole to activate the switch. Pick up flares to use later inside the treasure room. Since the switch is timed, quickly use the following steps to reach the treasure room: Return to the hole's entrance, then go Forward, Left, Left, Left, Right, Right, Left, Left, Left, Right, Right, Straight, Right. Run into house. The door is under the archway to the right when Lara first walks in the house. Once inside, use the switch to permanently keep the door open, then light a flare and explore. The treasure includes items from Tomb Raider and Tomb Raider: Unfinished Business such as the green cat and various idols.

Hint: Leaving the mansion:
Get to the point on the training course before Lara goes down the death slide. Walk to one of the corners at the edge and face forward. Turn about forty-five degrees and look straight down. While still holding the look button, jump straight up in the air. After the third jump Lara should be on top of the left or right pillar. From here, jump onto the wall, then run around it. Then Lara can jump to the roof of the swimming pool, maze, and even outside the patch of ground outside the gate. Note: If Lara goes outside the gate, she can not return.

Glitch: Elevator jump:
Walk up to any ledge that has a column next to it. The ledge would be shaped like an "L". Turn at an angle so that you are almost facing the column. Keep in mind that you should always stay at the edge of the ledge. Jump once and as you reach the ground, let Lara finish her "normal position" foot movement. Then, hold Jump to jump one more time. Keep the button pressed to will suddenly fly up to the very top of the column. You can do this on the training course of her house on the top of the last obstacle or level, and then explore.