Tron: Evolution

At the End of Chapter 3 on Casual

do not activate the switches which erases the floor

kill the 6 enemies...they'll respawn after a few seconds...just kill with the X-button until the achivement pops up

note: should be done very fast after you are fully upgraded

I know this game has been around for a while, and doesn't have a huge following, but after seeing the other 2 solutions, I felt I had another solution that works just as well, if not better. For those who still play, I think this approach will help "version up" (this game's way of "leveling up"), and help you blow through the Story mode on a harder difficulty to get those achievements too. Here goes:

1) Go into MULTIPLAYER
2) Go to CREATE MATCH
3) Go to GAME MODE SETUP
4) Set MATCH TYPE to PRIVATE MATCH
5) Set GAME MODE to DISINTEGRATION
6) Set MAPS to one of the following: HEAT SINK, HARD DISK, SPIRES, or SKYLINE (the last 2 are DLC, and all 4 maps do not allow Light Cycles. If a map allows Light Cycles you can't play against NPCs/Bots)
7) Set MAX PLAYERS to 10
8) Set TIME LIMIT to whatever you like based on what you set SCORE LIMIT to in #9
9) Set SCORE LIMIT to whatever you like in terms of how many derezzes (kills) you want to get
10) Hit Y to start the match.
11) Only use the X button for your attacks as the other buttons are special attacks, and your derezzes toward the total of 500 only count if you get them using X. Of course when you get the derezz the game doesn't say how you got it.

I have found this method quickest to get toward 500 derezzes, as well as a way to version up rather quickly, gaining those MB to perform SYSTEM UPGRADES quicker (thus unlocking the achievements related to these quicker as well). In addition, by versioning up and upgrading while doing MULTIPLAYER, your version and upgrades will carryover into the STORY mode, thus allowing you to go through the story on a higher difficulty to get the story-related, and difficulty-related achievements easier.

The above method can also be used for the achievements related to the various disc mods (Bomb, Corruption, Stasis, and Heavy) as well. You can do all this in a PUBLIC MATCH too against other players, that is of course if you can find one (lately there seem to be a few people on playing which is more fun than just bot bashing). Just remember, X is the key here. It's A LOT of button mashing, but given the 2.39 TA score, it's worth it.

I found the quickest way to get the 500 derezzed enemies is to set the difficulty to casual and start Chapter 7. Once you have made it onto the ship you can get around 40 derezzes with your disc quickly by killing everyone using only the X attack. When you get to the point where you are to jump off a platform onto a little walkway area you can exit and start the chapter over again.