The Guardian X-78 is an armor-weapon hero set.
The Guardian has a high shield level but a relatively low health level. The starting stats are at 250 HP and 350 Shield. At armor level two it has the ability to spawn 3 autoturrents. At level 4 your Autoturrent damage increases 100%. When you upgrade to level 6, you have the ability to summon "flamethrower" which is like a ultimate death ray trained at your target reticle.
The Defender is the Guardians only weapon. It shoots out small projectiles that fly relatively slow, but automatically shoots at enemies, much like an autoturrent would. It explodes on impact.