Going back to the Mega Man shield weapon thing:
Rock Barrier has offensive and defensive capabilities. When activated, Sigma is surrounded by eight small rock projectiles that briefly surrounds him to form a protective ring of rock that damages any nearby enemies that touch it. Each rock has a max HP of 112.5, making the barrier 900 HP max. The rock projectiles can deflect Primary Fire projectiles thrown at Sigma, & he can also fire these rocks at a fixed distance of 10 meters that do 9 DMG per shot. Firing all 8 will put out a maximum of 72 DMG.
The downsides is the more you fire, the less protection you get from the rock barrier. These rocks can only absorb so much damage before they are destroyed, and can only be fired in one fixed direction (think Doomfist's Rocket Punch). This barrier shield can't be used with Gravitic Flux, as casting GF will cancel out Rock Barrier and will immediately go back to cooldown. This barrier can't regenerate, and Sigma's Hyperspheres are disabled when Rock Barrier is in use.
Not perfect, but I already created a much more interesting barrier ability than summoning a god damn boring wall of HP that flies about.