Just wanted community input about this nightmarish matchup. I'll write a few bullet points and then add more as I receive more responses.
Slayer vs. Testament is one of those matches that makes you sigh, mainly because Testament's entire game is focused on keeping you out of reach and beating you out in several situations...into pretty painful amounts of damage. I play against a pretty beastly Testament, and I can tell you, I don't win very often (that also has to do with my inexperience and lack of skill).
I'm just going to bullet off things that I notice:
-Random Dandies and Mappas will be punished by traps, so don't go around carelessly with those.
-You can, however, punish Tree set with a Mappa if you're quick enough and 2D if you're close enough.
-Your Ks and Ps will be crucial for disarming traps. Always keep your eyes peeled for the blown skirt and arm rip animations.
-Beating Testament is a test of patience. It's important to get a knockdown because Testament has poor ways to deal with pressure. Once you have him under your mixup, keep on pressuring and don't let up. However, if the gap is large enough, discontinue your pressure, as Exe Beast will trade or straight up beat out almost everything you have.
-As far as mixup goes, I like to stay grounded and aim for cheap, easy knockdowns. If you're feeling gutsy, you can dash through stuff like Exe Beast and throw him.
-Saving tension for DoT is a common practice. DoT flies through and disarms all traps, so watching for trap-set animations becomes important. If you land the CH DoT, your chances of winning greatly increase.
-Testament's mixup is vicious. Between 2K, 6P, 5D, and being bounced back and forth by FRC'd Exe Beasts, blocking will become quite the challenge. This isn't to say that it isn't impossible though, it just takes experience and focus. All of it can be blocked on reaction, just get used to the deceptive animations.
-Testament's reach is generally better than yours and right out of your 5K and 2HS range, meaning you won't be winning the poke wars. Advancing slowly by disarming traps and catching him while in trap animation is your best bet at getting in.
EDIT -- Added from the matchups forum (original post by POscrub):
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Page 03: Slayer vs. Testament
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Slayer Basics:
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Learning how to deal with and get around Testament's Zeinest (Webs) and Hitomi (Trees) is the basics of this matchup. Jumping in with a j. K on the way up, and a j. HS on the way down, the j. K will trigger Zeinests before Slayer is in range to get hit, and if j. H is blocked, the Hitomi will pass harmlessly underneath, this is the best way to approach them from the air.
Against this tactic, Testament has the option of K Phantom Soul and 6K, early on, you can IB the Phantom Soul for additional tension, and double jump to avoid the 6K. Once you have the tension, you can try to look for an opening to turn things around with a Big Bang Upper, or a K Dandy Step -> Pile Bunker.
Kenchan's comments:
Slight disadvantage. Testament has the upper hand in general, but Dead on Time and Big Bang Upper are just too good. Slayer hits like a truck, so it's definitely still a fight.
Picture: Against Okizeme that uses Zeinest, you can use K Dandy Step FRC to evade.
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Exploiting Gaps
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If Testament gatlings f. S or 2S into 2D, if you Instant Block (IB) the attack before the 2D, you can counterattack with P Dandy Step (214P) -> Pile Bunker. If he does 5S or 2S into 2H, doing the above to get a Pile Bunker is effective, however, countering with Big Bang Upper also works. If Testament gatlings any normal into H EXE Beast, you can reaction back K Dandy Step -> Pile Bunker to punish. However, if he did 2H -> H EXE Beast, you need to IB the 2HS.
Picture: Opening up gaps in Testament's gatlings using Instant Block to make him wary is important.
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Aim for the Dead on Time:
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If Slayer manages to land a CH Dead on time, that single hit might very well end up deciding the outcome of the match, so aim to punish an opponent for making careless autopilot decisions. Some common situations that result in a CH, if Testamnet does any gatling canceled into Set Zeinest or Set Hitomi, if he just tries to set a Zeinest in a neutral situation, there's many attacks that cancel into 2HS and 2D, so if you see any of those attacks, get used to entering the motion for Dead on Time after blocking them, so that if he cancels into a Set, you just need to tap the button to punish. Note, if Testament decides to Set a Hitomi (Tree)in a neutral state, the animation is quite hard to see, so it's not something you aim for often.
Picture: Look to attack when he tries to Set something. When you have more than 50% tension, you should be priming the super motion, all the time. (ED note: ALL THE TIME )
Note at the bottom: Slayer's Big Bang Upper can trigger a Zeinest and still be capable of hitting, so use it with good timing to bust through attacks that hit high, like Testament's f.S, 6K, and 2H.
That's all I can think of for now. Please add more!