In the Teamfight Tactics patch 10.12, there are many strong compositions leading the meta such as Marksman Space Pirates, Hyper Tech Duelists, Mystic Guardians,… and in recent days, Vanguard-Mystic has climbed to the top of the meta with its unique strength.
Here are the tips for using the composition that is currently “making waves” on the Challenger ranks worldwide:

First, at the beginning of the match, you should prioritize using a few combinations of champions such as Vanguard Corsair, Corsair Cannoneer, Vanguard,… with the aim of shaping the “framework” for the main team later on.
This composition can win or at least lose without taking much damage, especially if you are lucky enough to “hack” some gold with Corsair.

After reaching level 5, if champions like Bard, Jayce, and Cassiopeia appear, you can change your composition to start using the main team. At this point, if you have a Blue Buff, you can combine it and give it to Cassiopeia, and if you have Dragon Claw (or a magic resistance component), you can give it to Jayce.
The strength of this composition at levels 5-6 is extremely powerful with high damage output and exceptional durability. Cassiopeia at the back will continuously spam skills to burn the opponent’s health, with 700 damage (burning over 12 seconds) at 1 star, this Serpent Woman may not quickly take down an enemy, but surely the entire enemy team will be left with low health. At that moment, Darius’s slashes will double the finishing damage to Cassiopeia’s victims, bringing in a substantial amount of gold if you’re lucky.
In the frontline, if Jayce receives buffs from Vanguard and Mystic along with an ideal magic resistance item like Dragon Claw, he will become a “monster” very hard to kill. Finally, Bard serves the purpose of activating Mystic, gaining experience, and supporting or scouting for Cassiopeia – very convenient.

After reaching levels 6-7, you can add Karma to activate Shadow, along with Mordekaiser, while also buffing Jayce for better durability. At this stage, you should save money and level up after reaching 50 gold.

You can also temporarily switch to 4 Mystic or 4 Vanguard compositions depending on what champions are available on the board.
At this stage, you need to decide whether to roll at level 7 or save money to level up to 8 and then roll. Since the drop rate for the 2 carry champions (Jayce and Cassiopeia) is 35% at both levels 7 and 8, your decision should be based on your health, the number of champions on the board,…

If you decide to roll at level 7, then you can only rely on “luck” to get Jayce to 3 stars and Cassiopeia to 3 stars. However, if you choose to reach level 8 first and roll with the income, you can maintain a safer health level since now you have the buff from 4 Mystics for the Vanguard frontline to endure better.
In the backline, Cassiopeia with 2 items, Blue Buff and Rabadon’s Deathcap, will continuously burn her target’s health (usually to death) with both magic damage and true damage, plus skill and item effects will severely reduce healing or shielding effectiveness. The final item is Rapid Firecannon as it allows Cassiopeia to stand still and continuously use her skills without needing to move due to her short attack range.

Finally, if you reach level 9, you can consider adding champions like Thresh (to activate Time Warp and pull additional champions down), Urgot (to activate the Combat Machine for Cassiopeia and finish off a target when using skills) or replace one Mystic champion with 6 Vanguards if the enemy team has strong physical damage.