I also have no idea how to open up people with Vergil.
.... you're kidding right?
LMH Stinger -> Rapid Slash = Cross up they have to block opposite
LMH Stinger -> Judgment Cut = Fake the Rapid Slash animation, catches them pressing buttons or blocking forward
LMHSH - Rapid Slash/Judgment Cut/Trick = Same as above, different string
Call assist during block string -> Trick M = Standard teleport + assist cross up
Call assist during block string -> Trick L = Fake the teleport + assist cross up
Call high hitting assist -> Activate Spiral Sword -> dash up and do crouching L's = Unblockable set up, even if they try to advance guard Vergil's fast wave dash + Spiral swords negates it. Can only be gotten out via cross over counter.
Crouching block strings + overhead assist (centurion arts) = Run of the mill unblockable set up
Random Helm Breaker -> Trick H -> Helm Breaker + assist call -> Trick L or M = Teleport mix ups with Helm Breaker. People like doing this with a low hitting assist, even though Helm Breaker doesn't hit overhead as soon as they see you port up they start to block high. With Devil Trigger on you can do Rapid Slash or Judgment upon getting them to block a Helm Breaker and they have to make the guess because you are at frame advantage in Devil Trigger after Helm Breaker.
Round Trip -> Trick M = Teleport as soon as the Round Trip is about to connect the opponent guarding. Self imposed cross up.
Round Trip -> Trick L = Same as above but you are faking the teleport cross up
Round Trip -> Trick M -> block string -> Trick M or Trick L = Double Round Trip cross up set up. You throw Round Trip and Trick before it hits them. You do a couple of hits while Round Trip is coming back to you and before it reaching you, you do another teleport changing the direction of the RT. You can do cross up or fake cross up. You can see this being done in the video I provided above. You can combine this assists for even dirtier set ups.
Helm Breaker -> Trick H -> Starfall on cross up = Trick H usually puts you in decent position to attempt a cross up with Starfall
During Devil Trigger -> Air dash -> Starfall on cross up = You can use air dash to attempt cross up with Starfall. Not that great but worth mentioning
Dash under st.H or st.S into Upper Slash series = Standard dash under cross up with Vergil due to insane hit box of Vergil.
Instant overhead (works only on tall characters) = j.L especially during Spiral swords
Resets
Upper Slash reset = During combo, add HSH after you have used up your ground bounce. This will put opponent in a soft knockdown roll state and they have to instantly roll back or forward. You can cancel the H into a teleport + assist call. Trick M catches them on the back roll and Trick L catches them on the forward roll.
Rapid Slash/Judgment Cut + Upper slash reset = Same as above only you attempt to mix them up with Rapid Slash or Judgment Cut after HSH.
Stinger reset = During combo, add a 2nd Stinger to your combo to initiate a psuedo-wall bounce and teleport. Teleport M crosses them up and Teleport L fakes the cross up. They are in an aerial state so you can also go for air throw or dash under cross up.
The "Wesker" = During a combo, add a st.L and immediately go for a Helm Breaker d/f+H OS with air throw. They block, they get air thrown... they press buttons they get high priority Helm Breaker to deal with.
The Vergil loop = Instead of going for the Helm Breaker OS you can do j.M, j.M, j.H into combo of choice just like Wesker to catch them pressing buttons. Delay the hits just like Wesker.
Spiral Swords dash under cross up = During combos you can opt to drop the Spiral sword loop to attempt a reset. You can dash under them with Spiral swords on and have the swords hit on the opposite side which is an instant cross up. Works extremely well on in coming characters as well. This is a bit tricky to set up mid combo, you need to knock them up high enough with something like Hightime
Rising Sun reset = End combo with Rising Sun into Trick down, puts them in an air tech state. You can opt to go for various reset options from here as they are in a vulnerable state. Air throw, Helm breaker, MHS/MHS, Round Trip set ups, Spiral sword dash unders, assist + teleport cross ups etc.
Hightime reset = Same as above only the easiest to set up. This used to be day -20 Vergil reset set up.
Whiffed Lunar Phase reset = During combos it is actually possible to whiff the final hit of Lunar Phase but this leads into a possible reset/mix up situation very low to the ground that they have to deal with. Hit them with everything I have stated above.
Storm Sword set ups = A very expensive set up that is ONLY RESERVED for killing anchor characters (last character on team). With 2 bars, mark them with Storm Swords and then lock them down with assists, Judgment Cut and Round Trip. As soon as Storm Swords start hit... start teleporting and once you get the confirm start the combo. The meter here is well spent as it usually denies X factor comebacks.
Bottom line: Use numerous mix ups and resets in conjunction with other. You use the Upper Slash reset and they block it? No worries... use a block string and if they advance guard it toss out Round Trip into RT mix up. They don't advance guard... attempt Rapid Slash cross up. Experiment with what mix ups work for you and there are more mix ups/resets options to be explored especially when Devil trigger and Spiral swords are used.
And I have way more resets/mix ups than these... the ones that I mentioned are match proven. Most of Vergil's advance tools are still largely unexplored yet including Round Trip, Spiral, Blistering, Storm and Devil Trigger.