User blog comment:Carinodren/Back in SotN.../@comment-51642-20100829163912

That's a gradius shield (if you've ever played Gradius, you'd know what it is). Essentially, it's supposed to absorb damage and get smaller and smaller until it disappears. But I haven't been able to make any use of it, and if there's any trick to making it useful, i haven't been able to find it.