Shielded Octotrooper
From Inkipedia, the Splatoon wiki
Shielded Octotroopers are Octarian fighters. They use shields to protect themselves from attacks.
Strategy
To defeat Shielded Octarians, they must be distracted, making them turn around and show their vulnerable side. Distracting them with Splat Bombs, Burst Bombs, or Seekers, is an easy method as they will turn around in surprise. It is also possible to simply sneak around through ink while in squid form, as they are unable to notice.