The First Descendant Vestigial Organ Gley

Gun Gley build focused on survivability, low skill, ease of use and rocket spamming.
The last 2 slots on the vestigial organ you should put are "weak point sight" and "weak point detection". Which I have tested on the Devourer could kill him in 17 seconds. At point blank range it's a given, at a distance it might pose a challenge to land consistent weak point hits due to slow projectile speeds.

"Enemies inflicted with Electrocution take damage over a period of time, suffer weakened DEF and experience mild Daze"

Weak point damage only happens when the rockets itself lands precisely on the enemy's weak spots not the splash explosions accompanied by the rockets.

"shot focus" is acquired by combining 4 rare cerulean type mods. If you don't have it you can replace it with "walk a tight rope" to achieve similar effect albeit better but with a condition that you need to have your HP at 50% or below to activate it's boost. If you have "shot focus" but want a bit more dps you can use both and swap out "hp collector" at the expense of survivability. Although it is harder to manage your HP with "hp collector" to not over heal when you need to maintain it at 50% HP to guarantee the damage boost from "walk a tight rope".

You may swap "increased defense" for "shield conversion (DEF)" FOR THAT MEASLY 6% EXTRA DEFENSE WHICH AMOUNTS TO ONLY 1K DEFENSE DIFFERENCE FOR THE LOW COST OF 200K KAIPER AND 2M GOLD.

Obviously this build isn't the highest dps nor the best type for fighting colossi, but while this meta is outdated it is still the most fun and most brain dead way of enjoying Gley in my opinion. Massacre Gley will absolutely destroy this build no doubt. On harder colossi bosses it is pivotal to know when to stop shooting (when the frenzy meter is about to be full) or avoid damaging weak spots that your teammates had grappled on (you shouldn't destroy the part they latched on to), reason being that as one person latches on the weak spot and "hold then destroy" e.g shoulders, it will temporarily stop the boss's frenzy meter from building up so that anyone shooting at the colossi (not the latched weak spot) will not trigger the boss into invulnerable phase.

(Only if you exclusively use the vestigial organ and not swapping to other weapons) then it isn't recommended on a team play especially on harder colossi bosses which require coordination and precise aiming, to avoid destroying weak spots your teammates had grappled on that are vital for stalling the frenzy meter from building up.

Everyone likes Massacre Gley, but it requires practice and good reaction time to be used effectively*
because it's a glass cannon which encourages high-risk high-reward plays. You are going to die a lot.