Sshate

Hold shift to start sprinting, then hold R to charge Dragon Strike. Charge until the orb pulses once to cover the most distance. Then Cartwheel to cancel the recovery animation.

The 3 basic smashes (LR, LLR, LLLR) have balanced total DPS, when you include the time spent in normal attacks.
The key difference is stamina recover from 2nd and 3rd normal attack. So if you have full stamina, just LRRR, otherwise get some stamina with more normal attack in your combo chain.

Many smash openers can directly skip into 2nd normal attack that recover stamina, making the smash openers free to use. So there's almost zero downside to using them all the time unlike other classes.

If enemy is far away:
Dragon Strike -> Dragon Chain -> normal attack(s) -> Smash

Small repositioning then attack:
Cartwheel -> Cartwheel Strike -> normal attack(s) -> Smash

If you have SP to burn:
Active: Tiger Claw -> Smash
Hold down a direction while using Tiger Claw to chase a boss while doing this.

Diamond -> Cartwheel -> Diamond -> Cartwheel -> Diamond -> Repeat
Basically like Arisha, but this is sub-optimal for DPS for Lethor because Tiger Strike (Counter Attack) is a major part of Lethor dps

Option A: Cancel it with Cartwheels

Option B: Wait until the white glow in Lethor's body starts to subside. Then
L + Space to cancel and immediately block again.
R + Space also works but costs more stamina.
You have to hit L/R literally milliseconds before you hit space again. if your Lethor attacks instead of blocking, you accidentally hit space first (or your keyboard may have input delay longer than mouse).

If you're desperate, you can spam space and hit L at the right time, but it's better to practice while you're waiting in RAR or something.

After successfully blocking, you should
1) Immediately hit R for Tiger Strike
2) R or L very quickly after Tiger Strike
3) THEN you can block again.

The reason is that when Diamond blocks successfully, its animation actually slows down so you need to quickly cancel it with a Tiger Strike by hitting R for sweet damage.
Furthermore, this yellow-damage Tiger Strike has recovery animation that cannot be canceled by Diamond. It can however be canceled into a normal/smash attack that can immediately be canceled into Diamond.

Sometimes, a boss would hit your with their main attack, then also spawn an AoE attack right after. You cannot deal with this like a multi-hit attack, since the two hits happen so quickly. Instead, you need to do the opposite and wait. When you successfully block an attack, Diamond's invulnerability extends a tiny bit, this is often enough to absorb the AoE hit.

Example of this is when Gate of Hell's Lavasat jumps and spawns AoE. If you stand right under Lavasat and block the landing impact but immediately counter attack, you will get hit by the AoE. But if you wait a little bit, Diamond will absorb the AoE damage as well, and you'll still be able to Tiger Strike.