Usually you have to sneak up behind someone to mind drain them, but there is a way to get a full mind drain off them even if they have seen you. Throw an enemy to the ground using TK or hit them with something to knock them over and use mind drain when they are on the floor, it wont work if they are standing up, unfortunately there head won't always explode but it will sometimes.
To use these cheats you must first use the appropriate code by pressing r1 on the extra content option of the main menu to unlock each charecter.
Better TK: Choose Edgar Barret in any one of his eight different skins to obtain a slower TK depletion, and to lift the train carriages and grey heavy boxes in the boss fight against him. MP3's will no longer be immune to TK and you will be able to lift and move them freely.
Better MC: Choose Jov Leonov to obtain slower MC depletion. This cheat will not effect the boss battle against him. MP3's will no longer be immune to MC and you will be able to take over their body's freely.
Better PK: Choose Marlena Kessler in any of her four skins to obtain slower PK depletion. This cheat will not effect the boss battle againt her.
Enter any of these cose at the Main Menu. Just highlight Extra Content the press R1, this will bring up the keypad, on which you can enter any of the following codes to activate the corresponding effect:
All Powers 537893 Arcade Mode 05051979 Bulletproof 548975 Co-op Mode 07041979 Dark Mode 465486 No Head Mode 987978 Super PSI 456456 Survival Mode 7734206 Unlimited Ammo 978945
The following codes unlock extra missions, just follow the same procedure as outlined above to enter the codes:
Aura Pool 659785 Bottomless Pit 154897 Bouncy Bouncy 568789 Gasoline 9442662 Gear Gauntlet 154684 Gnomotron 456878 Panic Room 76635766 Pitfall 05120926 Psi Pool 565485 Stop Lights 945678 TK Alley 090702 Tip The Idol 428584 Up And Over 020615
The following codes unlock extra skins, just follow the same procedure as outlined above to enter the codes:
Barrett 497878 Bikini Marlena 135454 Burned Soldier 454566 Clown General 431644 Dock Worker 364654 Dragon Wei Lu 978789 Fetish Pyro 231644 General 459797 Jack 698798 Jov Leonov 468987 Labcoat 998789 MP1 321646 MP2 698799 MP3 654659 Marlena 489788 Psi Sara 468799 Sara 135488 Saranae 65496873 Scorpion 546546 Soldier 365498 Stealth Nick 456498 Suicide Sara 678999 Tonya 136876 Training Barret1 196001 Training Barret2 196002 Training Barret3 196003 Training Barret4 196004 Training Barret5 196005 Training Barret6 196006 Training Nick 564689 Tranquility Wei Lu 654654 Urban Nick 484646 Wasteland Nick 975466 Wei Lu 231324