You can find slimes in flat areas at lease 6-7 blocks wide. Or in slime dungeons.
Chat with our AI personalities
In the bottom layers of the map or (if you have Weekly Snapshot 12w40a or above) in swamps.
step 1 find slimes underground (hint: look DEEP underground) Step 2 make the area where you found slimes easly accseable step 3 kill all the slimes step 4 leave and then later come back to kill more slimes step 5 ?????? step 6 profit
Yes, Slimes are hostile and will attack players on difficulties other than Peaceful (they won't appear at all in that), or Creative Mode.
Slimes still spawn, but only within 15 blocks above bedrock (adminium) and in large cavernous areas. If you dig down really far, and find a nice big area within 15 blocks of the bottom, you might find slimes. Another thing about slimes, is they spawn on any difficulty, including peaceful, but only the small one's will spawn on peaceful. There's a glitch where big slimes don't de-spawn when you change the difficulty.
Slime balls are only dropped from slimes. Slimes are green, gelatinous and very rare cubes, found far below the ground level.