Your Arena

[Apollo]

Arenas are pretty important for plenty of things in the game. The moon events almost require you to build some sort of arena.

My arena is built for multiple things. Invasions, moons and afk farming. It has a lava pit, commonly used in most of the moon arenas, lots of flamethrower traps, spiky ball traps, a platform on the top and super dart traps from the sides(not in the screenshot). Although it could have been made a little bit better, it works quite good for almost everything.
I would love to see other arena designs, so feel free to share yours in this tread.
Also, this works incredibly well if you are farming for keymolds, currently optimized for 3 biomes (Crimson, Corruption and Hallow). With just a simple spray of the clentaminator, you can easily farm the keymold you wish to get. It also works great for other item farming.

 

[DicemanX]

You can set up your arena to farm for all 5 key molds - no need to limit it to just 3. Add 80 Lihzahrd Blocks and 300 ice blocks (you can use purple, red, or pink ice to double up on blocks needed for all the biomes) and you're all set. Speaking of optimization, traps do piercing damage so they all interfere with each other - you can get away with just using a super dart trap battery along the bottom surface for very rapid kill rates.

If you want to check out other farms/areas, check out the following threads:

Autofarming Guide:
http://forums.terraria.org/index.php?threads/autofarming-guide-the-ultimate-chain-autofarm.3244/

Here's a video of 5 autofarms all chained together:

Moon Event Autofarm:
http://www.terrariaonline.com/threads/how-to-build-efficient-autofarms-for-moon-events.152527/

Here's a video showing the current record with video proof for a Pumpkin Moon fully automated autofarm: wave 15 by 11:10pm

Frost Moon Semi_autofarm (horseman's Blade farm):
http://www.terrariaonline.com/threa...eaching-the-final-wave-in-record-time.154083/

Here's reaching the final wave in record time with video proof:

And my personal favorite, the all-boss HM grinder:
http://www.terrariaonline.com/threads/duke-fishron-afk-autofarm.154031/

Here it is in action: