PSI Shield is a PSI spell used in all the Mother games.
PSI Shield destroys, or lowers the damage done by PSI. It can take three hits normally, but if a PSI Shield-breaking spell, such as PSI Thunder is used, the shield and attack cancel each other out. PSI Shield is useful against enemies with powerful PSI, like Fassad or Porky.
 Mother 2
In this game, Paula learns PSI Shield. This PSI Shield comes in two forms: PSI Shield α, which guards one ally, and PSI Shield Σ, which guards all allies. This PSI Shield destroys the PSI attack that hits the shield three times. It can be broken by PSI Thunder, which cancel each other out.
 Mother 3
Lucas learns PSI Shield in this game. Similar to Paula, he learns two forms: PSI Shield α, and PSI Shield Ω. PSI Shield in this game lowers the damage done by a PSI attack by 50%. Omega, similar to Sigma, guards all allies.