Viper skill page is a complete mess.

[PK_THUNER]

Normal Combo always starts with two skills on Combo 1 which is either a raw damage attack or a Debuff attack that makes the enemy take +10% more damage.

Then skill 2 is just use any of the two Combo 2 skills. The order does not matter since the one you did not pick will be your next Combo 2 skill.

Skill 3 is the one players need to pay attention on because the color of Combo 3 skill determines their position for flank or rear. Red skills are Rear attack skills and Green skills are Flank attack skills.

Then end the combo with the Finisher skill being the skill that is Serpent's.

Aso just just some stuff i noticed.

The 2nd parts of the combo will determine the positional of the 3rd part of the combo. So if you use skill 1 it's going to be flank, skill 2 will be rear. Because of the way your 3rd part combo buff works, it forced the 2nd part of the combo to alternate.

The 3rd part of the combo will buff 1 of the 4 3rd part combo. In practice it looks like this 2-1-1-2.
Your starting position in this sequence will depend on your first combo. I prefer to start with 2-2-2.

Now if we put these together with my stating point
It will look like this. 2-2, 1-1, 2-1, 1-2. You can see a patern here where you press the same button twice and when if crosses. Here's its, double press, double press, cross, cross. And this is how you can memorize the combo.

My full combo would be
2-2-2, 1-1-1, 1-2-1, 1-1-2.

[Jag227]

(CONTINUED IN REPLY TO THIS POST)

Now that we understand the theory, we can simplify the rotation to simple 1 or 2 button inputs. This rotation properly rotates between the 4 finisher skills. Full rotation:
1 - 1 - 1
1 - 2 - 1
1 - 1 - 2
1 - 2 - 2
REPEAT

To prove this is correct, place the 2 combo buttons (Steel Fang on 1, Dread Fang on 2 on your bar and press them according to this order. You will see this is the correct sequence of the "hit the glowy buttons" theory.

Now, notice how we never once used the skill Dread Fang - button option 2 during Step 1. This skill applies a 10% Damage Taken debuff to an enemy for 20 seconds (a very important ST damage debuff!) However, adding this skill into our rotation complicates it to an unimaginable degree. This skill is the reason Viper appears so incomprehensible. Watch what happens when we account for this skill. Since the debuff lasts for 20 seconds, it must be applied every 3rd round of our rotation (for optimal setup and 100% uptime)."2" in Step 1 represents "Dread Fang" The full rotation becomes:

2 - 1 - 1
1 - 2 - 1
1 - 1 - 2
2 - 2 - 2
1 - 1 - 1
1 - 2 - 1
2 - 1 - 2
1 - 2 - 2
1 - 1 - 1
2 - 2 - 1
1 - 1 - 2
1 - 2 - 2
2 - 1 - 1 (here for illustration, not meant to be used before Round 1)
REPEAT

This is what happens when you account for Dread Fang and maintain the pattern of alternating Step 2 every round and Step 3 every other round. Notice how we don't arrive back at our first round (2 - 1 - 1) for so long. Dread Fang alone transforms a 4-round rotation into a 12-round rotation.

(EDIT: The following is incorrect and corrected by @Shurrikhan)
Now, the debuff provided by Dread Fang - Noxious Gash - can be provided by another skill available to Viper - Dreadwinder. This skill holds 2 charges and refills every 40 seconds. Since each charge applies a 20s debuff, and we have 2 charges, we can achieve 100% uptime on the Noxious Gash debuff simply by using Dreadwinder ASAP when it becomes available. Also, this skill starts a separate combo chain which is far more powerful than our basic weapon combo anyway, so this leads to maximum damage potential.

From this, I can only conclude that Dread Fang should never be used. It is a wasted skill and only exists as a necessary placeholder skill for the 3 potential future skills that it morphs into as part of this single-button combo system implemented in this Job design. With the conclusion that this skill should never be cast, the Job becomes a lot more comprehensible to me. (Of course, I am exaggerating when I say it should "never be used". It can have utility when used to reapply that debuff to a new target on short notice.)

[Jag227]

However, I find it impossible to track even the 4-round rotation. I cannot keep straight a rotation with such an alternating pattern. Step 2 alternates every round, and Step 3 alternates every other round. I forget which skill I just pressed all the time. In practice, this rotation feels impossible to keep track of, and almost forces you to play the "hit the glowy button" playstyle. It's far too complex otherwise. Especially when faced with complex boss mechanics. I would prefer to focus on the boss mechanics rather than be required to look at my skill bar constantly.

I would love to hear other's input on my thoughts. I'm happy to clarify, and explain other aspects of the Job as best I understand it, if needed. Perhaps 4 finishers is too much. For example, the AoE rotation is much more manageable with it's 2 finishers.

[PK_THUNER]

Yeah that sounds about right. You either have to memorize the 4 set of combos or 2 set and then reverse it for the next 2 set.

[Shurrikhan]

ST Fangs, AoE Maws.

Open first combo with Death's Design Noxious Gnash (+dmg taken from you debuff) via Dread Fang for 20s, then pick either Jinpu Hunter (Damage) buff with flank finisher or Shifu Swiftskin (Haste) buff with rear finisher. Thereafter, alternate, but using Steel Fang over Dread Fang except as needed to maintain Death's Design Noxious Gnash.

GCD-CDs (Winder/Pit buttons) open into Void Reaping/Cross Reaping Hunter's/Swiftskin where Hunter is again flank and gives Jinpu and Snakeskin is again rear and gives Shifu, again to be alternated (opener, A B; opener B, A). They also apply Death's Design Noxious Gnash for 20s while having a 40s CD, so that further reduces the number of Dread Fangs you have to use, though wholly overcapping on the debuff costs only 60 potency anyways, a la Armor Crush.

So ultimately you just have to remember whether your spammable combo finisher was most recently Flank or Rear and whether your GCD-CD combo finisher was most recently Flank or Rear... and alternate.

Now, the debuff provided by Dread Fang - Noxious Gash - can be provided by another skill available to Viper - Dreadwinder. This skill holds 2 charges and refills every 40 seconds. Since each charge applies a 20s debuff, and we have 2 charges, we can achieve 100% uptime on the Noxious Gash debuff simply by using Dreadwinder ASAP when it becomes available. Also, this skill starts a separate combo chain which is far more powerful than our basic weapon combo anyway, so this leads to maximum damage potential.

No, you cannot. Charges do not cool simultaneously, so only the actual recharge time matters for something's relative uptime. Dreadwinder provides 20s duration on a 40s CD. Accordingly, it will take the place of every other would-be Dread Fang, not all of them.

[Jag227]

No, you cannot. Charges do not cool simultaneously, so only the actual recharge time matters for something's relative uptime. Dreadwinder provides 20s duration on a 40s CD. Accordingly, it will take the place of every other would-be Dread Fang, not all of them.

Ah, indeed you are right. Thanks. At least now I understand the context in which Dread Fang is necessary. That was seriously impeding my ability to understand the basic Job mechanics.

[Jag227]

Now I'm wondering if I am better off always using the Noxious Gash opener of both the ST and AoE combo chains. For the sake of simplicity. Just sacrificing the slight damage bonus of Steel Fangs and Steel Maw openers. Otherwise things become so complex and messy. For example:

ST rotation
2-1-2
2-2-2
2-1-1
2-2-1
REPEAT

AoE rotation
2-1-1
2-2-2
REPEAT

At least that is a static rotation that is somewhat possible to memorize.

[PK_THUNER]

I wouldn't. You loose 60 potency everytime you do that. Might be better to just "hit the glowing button" instead of memorizing it.

[Jag227]

Yeah, I just think I'd struggle looking at my skill bars so much, along with keeping track of buff/debuff timers and boss mechanics. Perhaps the Job is just not for me

[Kukajoo]

I do the bare minimum reading and then just press the buttons that keep the dots /buffs up then press the fancy fun buttons when my dots / buffs are fine, Viper in a nutshell

(By dot I do mean the silly red rpr adjacent more damage thingy not actually a dot but blehblahbluh)