Guilt Battle Arena

The fastest way I found to grind this was doing:
- Battle Arena
- Game Mode: Vote
This way you can avoid playing the rounds that take longer to finish. (Alien Pet, Parasites, Gold Rush, Hot Potato Bomb, CTF are the ones you want to dodge)
- Match Type: Championship, 20 rounds
- Arena Type: Normal
- Bots: 1, Easy

You can then simply either kill the bot or kill yourself, whichever is quickest depending on the game mode. (I.e. in Cat Mania/Fatal Dodgeball killing yourself is quicker than killing the bot)
Doing it this way I was getting through 20 rounds in about 6-7 minutes.

This Achievement is much easier with a controller with a turbo function or an accessory like the Mayflash Universal Adapter Ultimate (which adds turbo to an existing controller). If you don't want to purchase such a controller or accessory, you can still do this by jamming away on the button for hours.

First, complete every other Achievement besides the "Play X rounds in versus" Achievements. That should allow you to unlock all characters, thus preventing the character unlocking dialog from interfering with the automated nature of this technique.

Second, select these options:

- Custom Game
- Game Mode: Chicken Rain
- Match Type: Winner Takes All
- First to: 10 rounds
- Bots: 1
- Bot difficulty: Hard

Third: Activate autofire or turbo for the so it's continuously being pressed. If you don't have a turbo controller or accessory, just press repeatedly for hours while you do something else, like watch television.
Let the bot defeat you over and over until the Achievement unlocks.

Each round will be about 5 seconds. Each match will be 3 - 4 minutes. You will need 25 Matches overall.
This should be an hour and a half, if you're pressing when its needed.

- Custom
- Game Mode: Last Man Standing
- Match Type: Championship
- Epic Match
- Speed-up & Fast Bullet: On
- 1 Bot set to Insane