Resident Evil 3: Nemesis Hints, Tips

Mercenary Mode

Finish the game once to get mercenary mode and save the next game file. Begin your new game, pick that saved game, and then select mercenary mode.

Alternate Costumes

Finish the game under the easy difficulty setting with any rank better than F to unlock, and an A rank will give 3 more costumes.

Epilogues

Finish the game under the hard difficulty setting(Getting better ratings can unlock the other epilogues)

Epilogue Files.

Every time you beat the game, you will unlock a different epilogue ending for previous Resident Evil characters. There are 8 in all.

Ada Wong - Beat the game 7 times.
Barry Burton - Beat the game 3 times.
Chris Redfield - Beat the game 2 times.
Claire Redfield - Beat the game 5 times.
Jill Valentine - Beat the game 1 time.
Leon S. Kennedy - Beat the game 4 times.
Sherry Birkin - Beat the game 6 times.
Special Agent Hunk - Beat the game 8 times.

See Director's Message.

After you unlock all of the character endings, you will see a special message from the director. One word of caution, this will be the only time you can see this.

Get New Weapons and Infinite Bullets in the Game

Start a game in Normal Mode.
Every time you beat Nemesis you'll get:

1 time: Eagle Parts A
2 times: Eagle Parts B
3 times: 3 Heath Sprays
4 times: Shotgun Parts A
5 times: Shotgun Parts B
6 times: 3 Health Sprays
Every time: Assault Rifle

If this is your second visit in the game(you finished the game and loaded your save)you'll get if you've beaten Nemesis everytime instead of the Assault Rifle the Infinite Bullets.Use it on one of your weapons and you'll have Infinite Ammo then.

Jill/Carlos Ending

When you pass through the bridge to Disused Plant, you face Nemesis. Choose the 2nd selection to jump out of the bridge. Then when finishing the game, you obtain an ending with Jill and Carlos.

Jill/Carlos/Barry Ending

When you pass the bridge to Disused Plant, you'll face Nemesis. Choose the 1st selection to lure Nemesis jump out, and run straight to the Plant. Then when finishing the game, you obtain the ending with Jill, Carlos and Barry.

Jill's Diary

To get Jill's Diary, collect all 30 files in the game in order then the 1st file (Instructions Manual) will become Jill's Diary.