Rattle Shake Base Upgrades
Rattle Shack Attack Damage Numbers
Rattle Shake Deputy's Duty Upgrade Path (Top)
Rattle Shake Coiled Ammunition Upgrade Path (Top)
Rattle Shake Bone Herder Upgrade Path (Bottom)
Rattle Shake Grave Springer Upgrade Path (Bottom)
Quickdraw Rattle Shake Full Upgrade Set
However, the Upgrade Paths will really change the course for your Rattle Shake. The top end comes down to a preference between the Primary and Tertiary attack, while the bottom end offers up pretty unique options, which much like Undead Swapper counterpart Night Shift, feature cool animations.
Deputy's Duty may seem pointless at first, after all you've already got it, right? That, however, is far from the case. Where "Deputy Snake" hits with 20-30 and then proceeds to spit venom that does 12-18 Damage 14 TIMES, by the time you've added "Nasty Sssurprise" and "Armed to the Fangs" those numbers have surged to 30-45 on Impact and 16-24 on the 14 Venom Hits. That is a very substantial increase when you do the math. The biggest asset may not be the cumulative damage, but rather the fact hit enemies are slowed down! I find this to be very effective. The snakes home in, but if you are unhappy, just toss another one out and take advantage of the acid splash on impact.
Coiled Ammunition is two fold. "Snake Bite" poisons the first enemy "Spring Loaded Snake" hits and causes it to take damage (8-12 3x) over time. "This Bites" is the follow up and has those "poisoned" enemies take extra damage from your primary attack at 24-36 instead of 20-30. While I love the 45-68 on the first hit and the unique ability to pick up items along the way, there are two big downsides here. First, only the first enemy is poisoned. If the poison chain ran along every enemy that the snake ricocheted off of, it would be a different story. Second, and tying in with that, the "first hit" poisoned enemy only takes 8-12 damage 3 times. Yes, I know that they take more damage when I shoot them, but the +4/+6 is lacking when you consider that you will only have a few ticks of the clock to cash in..By then, the enemy has pursued you and you will have to retreat, or just use other attacks...likely not being a charged attack of any sort, which rules out the Coiled Ammunition Path. I feel like if the snake ricocheted AND did maybe 5-8 hits of damage to give you a bigger window to cash in on things would be different. As is, Deputy's Duty does more damage, 11 extra times, and SLOWS enemies...I have to give it the edge here.
The Bone Herder Upgrade Path introduces a "Goliath Bone Snake" that you charge up and release. This summons a literal giant, bone snake from the ground that springs upward off the screen. With Damage Numbers of 90-135, this is the "big hit" some people are drawn to...The next installment "Dances with Snakes" has you move around to conjur smaller snakes that follow the same mechanic. These auxiliary bone snakes will do 60-90 Damage. This one is a lot of fun, but I have found that in tough situations your likely only going to be able to get the "Goliath Bone Snake" to launch at your intended target. If you aren't as concerned with accuracy, but rather fun, it can't be beat and when it does make contact it deals incredible damage.
The Grave Springer Path isn't quite as dramatic, but it is effective with cool artwork of its' own. "Spurred Spring" let's you charge up quickly and spring into the heat of a fight. This deals 40-60 damage, but is complimented with "Graveyard Smash" (contestant for best upgrade name ever) which spawns roughly 5 Tombstones when you land and inflicts 25-38 Damage. Obviously, with 5 tombstones in play, this has a pretty nice area. The scenario would be you have deployed your top end initiatives and then spring forward towards the target enemy and "Grave Springer" does auxiliary damage. Put it together and you have, at minimum 65 Damage, with the possibility of 98 and additional damage/kills depending on what enemies lurk around your target.
Before we cover my suggestions, I have to stress that both top and bottom Soul Gems, "Raise the Snakes" and "The Snake-Skinned Kid" respectively have a red flag. While the Critical Hit and Speed boosts are great and the animation/concept is unique and very fitting, there is an aesthetic change. I will warn you in advance that both of these Soul Gems turn their respective half of Rattle Shake purple. I actually don't mind the change...it is menacing and somehow very "Undead," however, I also really liked his box-stock aesthetics. Plus, being from Texas and dealing with Rattle Snakes, I have a hard time with the purple...Some of you will love it, some will hate it...most will just want the benefits of the Soul Gems and not really care. However, amongst the hard core fans I know these aesthetic changes matter. Rubble Rouser, Dune Bug, Pop Thorn, Prism Break, even Slam Bam's Yeti Cooling Factor have had a long track record of angst for select Portal Masters. I am fortunate in that I have the extra Rattle Shake and could leave him Soul Gem-less. If you have Quickdraw you are in a tough boat...Do you max out your prized variant, or do you let him go without Soul Gems to maintain his unique look? It is up to you...I personally went with a combo, lol.
For rookie players I would suggest you go with Deputy's Duty and Bone Herder. Deputy Duty is a compliment to both Snake's Venom and Tail Sweep (and all their other upgrades). It comes in VERY HANDY. Bone Herder will take some time to get good execution collectively, but I feel like the prospect of getting good with one Goliath Snake is more beneficial to rookie players than Grave Springer as you can still retreat.
For veteran players I would suggest Deputy's Duty and your choice of Grave Springer and Bone Herder. Grave Springer may seem a bit more "dangerous" due to flying in towards your enemies, BUT just like rookies needing to perfect "Dances with Snakes" this isn't the easiest upgrade set to cash in on...
Personally, I think the ideal combo is Deputy's Duty and Grave Springer. Deputy's Duty is a no brainer and super effective (as long as you remember to use it). One of Rattle Shake's best moves, in my opinion, is simply hitting enemies with "Armed to the Fangs." I like to do that, let the snake run it's course and then go about my business with the other attacks. Grave Springer wins out for me because I can use "Ssstampede" to soften up a target, rush in with "Spurred Spring," get bonus damage from "Graveyard Smash" and then repeat the process to get out of harms way and set up the next attack. This has a much higher hit rate than "Dance's with Snakes." I do miss Goliath Bone Snake with this set, but I feel it is made up for with the success rate.