Gnosis

General overview

Gnosis' banner introduced the cold/freeze mechanic, which his kit uses to full effect. Freeze is an incredibly powerful status effect on its own because it stops enemies from acting and has a built-in RES debuff, but he introduces damage amplification to the mix to make it hurt even more than necessary. He's surprisingly good for general use and can serve a variety of unique roles depending on what skill you use. His only downside is that he can't debuff anything that's freeze-immune, but there are so many terrible enemies that aren't, and you'd be hard-pressed to find a more efficient (and probably unethical) way to deal with them.

Before I am accused of bias here, I want to clarify that I don't like Gnosis. This man broke into my house and robbed me.

E2? Gnosis certainly isn't an early-game fast track E2, but, like the other members of his archetype, he requires it at some point to be used effectively. His primary means of debuffing, fragile, is almost doubled at E2, and his skill 3 is incredibly powerful.

Game modes

Gnosis has more versatility than the other debuffers because his DPS is leagues above them, and he has some built-in crowd control in addition to his debuffs. He's an excellent CC pick because nearly all enemies that will give you trouble are susceptible to freeze, and he can give your team a lot of extra breathing room in addition to the handsome debuffs. In IS, he's not a bad pick in general, but his power level spikes with certain supporter relics as well as the ones that do arts damage per second to frozen enemies. And in SSS, he performs fairly well at low levels with no buff stacks, but buffing him turns him into an absolute monster. Caster stacks are a good choice for any of his skills because the extra SP improves his already good uptime, but sniper stacks are also an appealing option if you want him to be able to freeze enemies with his normal attacks.

Talents

Talent 1 - Rigid Ice

E1 Attacks inflict Cold for one second. Apply 15% (+2%) Fragile to Cold enemies within range. Frozen enemies within range receive double the Fragile effect

E2 Attacks inflict Cold for one second. Apply 25% (+2%) Fragile to Cold enemies within range. Frozen enemies within range receive double the Fragile effect

This talent is central to his kit, although the cold that he inflicts on normal attacks isn't long enough to do much in most circumstances. The fragile effect is similar to Suzuran's talent 2 in the sense that it applies to any enemy inflicted with cold/freeze in his range, regardless of who the dealer was. He pairs great with other cold-inducing operators for this reason.

Talent 2 - Two Paths, One Goal

E2 Grants Status Resistance to all Karlan Trade Operators after being deployed for 10 seconds

Status resistance is always nice to have. Faction buffs can be a bit tricky if you don't build your team around them, but worst case he's at least granting it to himself.

Skills

Skill 1 - High-Speed Cogitation

Skill effect: The next attack deals 150%/170% ATK as Arts damage and attacks twice consecutively

Overview: This skill looks like filler, but it's an incredibly effective single-target crowd control/DPS skill. It gives you a guaranteed freeze, and keep in mind that the fragile from his talent will apply for a little extra damage. It doesn't extend his freeze duration at all, though, so think of it more as a brief attack or movement interrupter than sustained crowd control.

M3? Please don't do this. Sincerely, someone who did do this.

Skill 2 - Zero-Point Burst

Skill effect: Deal 160%/200% ATK as Arts damage to all enemies in range and inflict Cold for 3/4 seconds. Charged effect: Inflicts an additional layer of Cold

Overview: This skill is incredibly powerful but often overlooked due to how flashy skill 3 is. It's a little harder to use, and it gives him the worst DPS out of his skills, but in exchange you get an on-demand 4 second true AOE freeze with excellent cycling time. 4 seconds is more than enough time to give your team some breathing room, and he'll be ready to go again in no time at all (8 seconds from the end of the freeze at M3).

M3? I kind of have to advise doing skill 3 first, but you should definitely come back to this skill if you use it. He doesn't get the reduced SP cost or extended duration until M3, so it's mandatory to squeeze as much uptime out of this skill as possible. You also get a nice addition to the damage multiplier.

Skill 3 - Hypothermia

Skill effect: ASPD +122/130 and attacks 2 enemies simultaneously. Extend the effect duration of Frozen enemies within range until the skill ends, then deal 400%/600% ATK as Arts damage to all Frozen enemies and remove the Frozen effect when the skill ends. Prioritizes enemies that are not frozen.

Overview: Everything in this skill description reads like it's too good to be true. Yes, he can freeze everything in his range for up to 13 seconds. Yes, the SP cost is pretty low for what it is. Yes, he does a ton of damage over the course of it before finishing it with even more damage. Skill 3 is Gnosis' marquee skill for a reason - it's a real monster of a crowd control skill, and let's not forget about the debuffs: -15 RES from the freeze and 50% fragile from his talent (which also applies to the massive hit of damage at the end!) It can do everything except your laundry and probably your dishes.

M3? M3 does a lot for this skill on multiple fronts - it increases its duration, reduces its SP cost, further buffs his ASPD, and adds a whopping 200% attack to the last hit. You need M3.