Lambda is a character that excels in keeping her opponents at a distance and overwhelming them with her swords. Her poking tools include most of her "D" attacks, and 5A and 2A to poke out of pressure. Her normals are decent, with 2B and 3C used as fast long range attacks that can catch the opponent off guard. With most matchups (Rushdown characters like Ragna and Jin), you'll want to focus on zoning the opponent out until you've depleted them of their health. For characters that are also zoners, or that have a stronger neutral than you (Rachel, Nu, etc.), rushing them down and keeping them locked down with oki would be a more preferable approach than trying to one up them at their own game.
As a zoner, Lambda's Spike Chaser, Sickle Storm, and D strings are decent for keeping the opponent at bay. But, her shortcoming is that these tools do not open a competent opponent up often. As a result, leaning only on Lambda's zoning can spell disadvantageous if your opponent can see the openings in your zoning and is patient.
With that being said, Lambda's mixup and pressure tools are also sub-par in that she cannot open people up easily with her normals. 6B and TK j.214D are her only overheads, and can be mashed out of. As far as pressure goes, her 2A can be use to setup stagger pressure, tick grabs and TRM setups, these options are not very strong either.
In short, switching between the two spectrums of heavy zoning and rushdown will keep your playstyle fresh and also keep the opponent guessing on what you're going to do next. In the end though, figuring out a combination (or bias towards one way of playing) that works for you is key.
For more information on how to use Lambda, please refer to this in-depth strategy guide: http://www.dustloop.com/forums/index.php?/forums/topic/11069-cpex-lambda-11-strategy-guide/
Lambda can be a very aggressive character by utilizing the right tools. Once you get an opponent blocking a D string, you can rush in with 236A and pressure them with her normals like 2B and 2A until you open them up. Ending combos with Blade (236B) allows you to set up Sickle Storm and continue the offensive onslaught with more D's or close range normals. The idea is to fluster your opponent with D's until they've been opened up, and eventually pushed into the corner.
The corner is where Lambda nets most of her good damage, and after every combo oki can be established to keep the opponent blocking. Sickle Storm is the cornerstone of your offense game, as it chips the opponent and allows you to get in and mix up them up with overheads, throws, and everything else in your arsenal. With every non blocked D string combo ending 236B, and every normal based starter combo ending in 236B, your opponent is pushed further to the corner and forced to take more mixups while blocking Sickle.
The general idea is to keep this rhythm up while maintaining an airtight neutral, half of offense is being able to throw D's where the opponent will be so that they're continuously blocking.
Lambda's defensive options are limited, and as a result, being successful depends on your ability to use your mobility and swords to dance around and keep the opponent at bay. With no meterless reversal to fall back on, being able to perform those two actions is crucial if you plan on surviving.
Lambda's main reversal is Calamity Sword (632146D), where she summons an overhead sword next to her. This is a decent reversal, as it deals a solid 2K damage on regular hit, and can be followed up with a combo on counter hit. The only downside to this reversal is that it loses to other reversals and call outs, such as; Ragna's 623C, Jin's 623C and Yukikaze, Relius' 236A and others. You do not want to be too deliberate when you choose to use this reversal.
While Lambda may be light on reversal's, she is quite armed when it comes to anti-air attacks. Her main AA's include 2D, 6D, 2C, and 6A. 2D and 6D are your go to choices, for they can catch an opponent from a far distance without committing too much. 2D shoots a sword at a 70° angle, and goes upward at a deep angle, a good choice for when the opponent is close or above you. 6D shoots a sword at a 30° angle, and goes fullscreen. This is more suited for when the opponent is not very close, or attempting an IAD. 6A and 2C are last resort options when the opponent is too close to use 6D or 2D. 6A offers head invulnerability, while 2C has an overall decent hitbox.
Neutral is where Lambda truly shines, as the tools you have at your disposal to hinder your opponents approach have the most effect here. 5D and other D strings is what you'll be using the most to provoke a response out of your opponent, and the options after a blocked D string are plentiful.
Spike Chaser covers half of the screen, and will force an opponent trying to get in on you to block it, or get hit trying to jump over it. Once the opponent blocks it, you can continue with more D pressure. Spike chaser is an invaluable tool because it stops the approach of rushdown opponents, and can also eat projectiles like Tager's Spark Bolt and Kagura's orbs.
Sickle Storm is a circular saw that appears in front of the opponent and hits multiple times. Sickle has amazing chip properties, being able to whittle down the opponent's health if they're not barrier blocking, and even then eats barrier at a fast rate. While the opponent is blocking Sickle, you can deploy a Gravity Seed, summon Spike Chaser, or advance on their position with 236A and try to mix them up. Attempting to chip the opponent out with sickle is a doable and common tactic among zoning oriented Lambda's.
Gravity Seed is a field that slows the opponent's movement speed, effectively slowing their approach, and buying you extra time to set up Sickle Storm or Spike Chaser. As you've probably noticed by now, these three specials will aid you the most in making your opponents life harder, and your zoning easier. Besides these, Act Parser Zwei is a special that teleports you towards the opponent, at closer distances towards your opponent, you can cross past them. This is handy for when you get the opponent blocking while you're in the corner, allowing you to get back to neutral. It is helpful for situations like that, and others that you come across.
Legacy Edge is a good distortion to use when neutral isn't going your way and you wish to reset it's pace to your favor. While the opponent is blocking that, you can use Sickle Storm and Gravity Seed to keep them at that spot long after the distortion ends.
In summary, Lambda has dominating neutral tools, but being able to zone your opponent out with D's requires knowledge of where you feel the opponent is going to move and being able to predict and react consistently. Lambda can get blown up pretty quickly if you don't have a strong grasp on neutral and how to effectively zone out each character depending on the matchup.