DeploymentSo lets talk about the deployment of the list. Start with deciding where Vayl2 will stand. She wants to be in the middle-ish and have a way to walk 8" and shoot 14 without terrain being in the way.
You want the AA and Seraph close to your caster. This is since our turn 1 move is to empty ourselves. Then you want the AA to run and cover LoS to Vayl2. Since Vayl2 walk 8" up with slipstream and the AA runs 14" and the AA base is almost 5" we do not have much marginal for when the AA runs past Vayl2.
The next part of deploying Vayl2 correctly is to see where you need to deploy the Hell Mouth. The primary objective here is to make sure it is safe. The pressure of one free arcnode will let you win most grinds. Keeping it safe is a lot more important then restricting where your opponent can put a heavy and then losing the Hell Mouth.
I know this is a bad example since I deployed the Hell Mouth on the line but my opponent was playing a really slow Khador list and had no way to really threat an occultated hell mouth.
The plan when you startSo the first thing I do when I start is to check what I can reach. 31,6 for 8" spells. 33,6" for Deadly Storm. Then I check if it's worth it to feat. Can I get enough value out of the feat right now. Can I kill the whole choir for example. Can I kill Cassius and some stones. Mostly it's about will the feat will deal more damage turn 2 then right now. This is kinda hard to know from here since your opponents list and placement will decide these things. In a practice game I would generally feat just to show my opponent what could happen and then they fix their deployment.
Anyway. First turn. Seraph Apparition up. Something kills a tentacle, usually a deathstalker. Vayl2 gets Slipstreamed and the Seraph charges forward. Then the Hell Mouth creates a new tentacle and place it into position. 20" with the back in front of Vayl2. 22" if you do the slipstream after anyway. In position to get a snowball in the back. Vayl2 walk up far strike for 1, or free on the feat, then apply spells as needed. Once again here this is depending on how your opponent sets it up. Hitting a unit with icy grip is kinda fun. Killing a packed low armor unit with 2 deadly storms is nice. Just bolting 3 things with chasten. Doing 2 chastens with boosted damage into a Warpwolf stalker is nice. Get some free value. If you need occultation on the Hell Mouth it's extra worth it to feat.
Then AA runs in front of Vayl2. Do not. I repeat DO NOT run inside of 19" of Caine2. Then you give him a huge base to bounce shots of into Vayl2. That will kill you. Then rest of your army runs full speed up the board.
His turn he will move around a bit. Nobody really cares.
Your top of two you can check. Are you feeling good about this match up or is it time to kill your opponent. How to find angles for assassinations take time. Luckily at this point you probably have 50 minutes to do this. Check if you can throw a model at them with the AA. They are trash remember that. They are trash remember that. Just kill them. It's easy.
Going secondGoing second generally sucks. You are a hit and run list and the sr16 scenarios are generally slow enough for you to lose the grind if you go hard for scenario. So don't do it. Just win the dice roll :D
In all seriousness Check what you can get in. Check what spells you need up. Then just run up everything just outside of his threat ranges. Turn 2 he does some stupid running to contest scenario and then you just fucking kill him. If you need tips on how to do it. Look above. It's a really simple throw chart. Can I kd caster then kd caster and kill him. Can I not kd caster and kill him check if you need to kd him? Yes you do so check again if you can kd him. Then just realize you can kd him and kill him.
Parting wordsDo not go for caster kills. I know I say a lot about it in the article but I'm a terrible player. Why are you even listening to my advice? Going all in for a caster kills is a terrible idea. A good player will only go for caster kills when you feel like you have lost the grind or they are standing so you can kd them and then more or less auto kill them. Even at those odds they protect against failure. Make sure you never let Vayl2 stand out in the wind for a 30% chance to kill caine2 top of one. Take it slow. Kill the support models, kill the jacks then kill the caster when nothing else is left.
One of the best skills in the game is to realize when you have won the grind and just take your caster and run it towards your end of the table.
Some easy math. A good assassination run is in the 80%-99% Lets say all rounds you get a 90% kill. Then after 5 round there is a really real chance that you have lost one of your games(40% ish). The people that consistently win tournaments don't let their caster die and never go for stupid assassination runs.