We're all used to the JJ2's set of three shields (and the disgrace to the entire shield kind known as the laser shield). They don't vary all that much between each other and don't leave much choice to level designers in the occasional cases they actually want to add a shield to their creation. Overall, the point I'm trying to make and I think we can all agree with is that the quantity of available shields is just not large enough.
We at the JJ2+ staff believe we have just enough control over the game code by now that we can fulfill the task as is adding a brand new shield to the game. And guess what, we decided to ask the community for ideas on what it could be, and that's exactly what this thread is for.
Now to help you organize your ideas here is a list of things that define a shield type:

• Visuals
  • Shield body - the main and most memorable part of a shield is the sphere around its owner. Even though all of the game shields follow this scheme, there is technically no reason for us to stick to the spherical shape so don't feel limited to it and just describe whatever you would like your shield to look like. When you consider colors, keep in mind certain JJ2 limitations - especially that in 8-bit mode (that we'd like to and will keep compatibility with) it relies entirely on its palette that has only so many constant entries. If you think a simple description is not enough, you can always draw concept art of the shield; it's far from obligatory but you would be sure to avoid any misconceptions.
  • Projectiles - every shield has its own kind of bullets it allows players to fire. Those, generally, use sprites, and a brand new shield requires brand new sprites. Again, keep in mind the JJ2 palette when you describe them. It's also hard to hide it would save us a lot of work if you actually drew the sprites yourself but if you don't want to, you don't have to.
  • Particles - those can only be observed for the fire shield and the lightning shield and are not an actual requirement. Particles are created by travelling and exploding projectiles but if you fits your theme they can probably be also left by the shield itself. Say what they should appear and behave like, possibly draw them if you feel like it; they're small so it shouldn't be much of an effort.
  • Shield monitor - there's not much freedom here, the shield monitor basically displays a small symbol that represents your shield. You can tell us what you think it should be or you can draw it yourself (the symbol itself is limited to the size of about 10x16 pixels).
• Mechanics
  • Projectiles - the only real difference between mechanics of various shields is observable in their projectiles. And yet, two of the existing shields introduce nearly no real changes compared to regular blaster. There's a lot of room to be original here. Tell us how much damage the projectiles should do, what their trajectory should look like, how far they should go and whatever other special properties they should have, anything that comes to your mind, really. Try not to describe a weapon too overpowered or useless - balance is the key. Like in other categories, describing this aspect with words will do completely fine but if you're feeling ambitious and are skilled with AngelScript, feel free to write a script that will demonstrate your desired bullet behavior.
• Sounds
  • Looped sound - the sound you hear constantly when the shield is enabled. Even though all existing shields do have one, it is not really obligatory, especially in case it just doesn't make sense for your shield to make sounds on its own. Provide a brief description of the sound or post a link to a sample.
  • Projectiles - they make sounds when they're fired and when they explode. No matter what your idea is it probably makes sense to have at least one sound made by shield projectiles. Again, describe the sound briefly or post a link.

Example:
If you wanted to suggest to add the JJ2 water shield, you would probably post something like this:
The idea that is considered by JJ2+ staff to be the best one is guaranteed to become one of our priorities and be implemented in one of the nearest versions of JJ2+ (I realize this might sound kind of vague; that's purely because we never implemented a new shield in JJ2+ and can't know how much time exactly it can take us). The winner, if possible to contact, will be kept updated with our progress implementing the shield (with pictures!). Additionally, every other shield idea posted in this thread will be considered and might be added to the patch later during its development.
Even if you don't have an idea of your own, you might want to post in this thread to comment or support others' concepts. Don't be afraid to express your opinion as it might affect the final verdict.

Because it's always difficult to tell what amount of activity and interest can be expected from JCF, there is currently no deadline. When the deadline is decided on, a proper post informing about it will be made in this thread at least a week before the contest is closed.

Good luck!