Hello everyone and welcome to my 211th analysis, this time featuring Warmaster Thalassa.
Overview: Thalassa is the queen of Monster Legends, and anyone who dares question her rule will quickly learn the harsh reality of what the best monster in the game can do. Thalassa is blazing fast at a Speed tier of 3542, outspeeding a vast majority of monsters in the game. Her trait includes Tough and it gives Freeze Immunity to all allies, which is crucial in Sea and Water Wars, and also doubles the Stamina of all allies for 3 turns, which can be used in interesting ways. However, what makes Thalassa so fearsome is her moveset: she has 2 AOE Mega Freeze moves in her arsenal, and moves that remove traits and buffs while giving her extra turns, arguably creating the best denier moveset in the game. The only downsides to Thalassa is that she is not godly among other deniers when not ranked up, and that when left alone, she cannot finish the battle - as you can see, two very obscure downsides. Thalassa is always a threat to keep in mind and prepare for, or you will be fighting a losing battle.

Builds:
Monsters that have access to Group 4 skills will have a slightly different build path. I will list the most viable builds for each Rank since some moves in Group 4 are pivotal to some sets' success. The monster's role will likely remain the same, however, so this won't be exhaustingly long as I won't repeat the same things.

Rank0:
Moves:
-Artic Waves
-Abyssal Pressure
-High Pressure Fluid
-Thalassa's Chosen/Ocean Rain
Runes: 3 Speed
Mutant Rune options: Speed&Life
Relics: Armors and Amulets

Build Explanation:
Artic Waves is your AOE Freeze move that also applies Drowned to all enemies, a damage dealing version of Stamina Leak. Abyssal Pressure is a single target Mega Freeze that deals AOE damage, which is useful in case it's needed. High Pressure Fluid is a very flexible and useful attack that removes all buffs from the target and gives Thalassa an extra turn; it can allow her to remove annoying buffs like Evasion and Mega Taunt. Lastly, Thalassa's Chosen can save an ally from all kinds of debuffs while giving them Freeze Hater - useful after Abyssal Pressure has been used. Ocean Rain is an alternative here to cure the entire team and also not get countered by Anticipation users.
3 Speed is mandatory on deniers, while Speed&Life are the most viable Mutant options.

Rank1: Thalassa learns "Cryotan Breath" at this level, a Base 35 Water AOE that Mega Freezes all enemies.
Moves:
-Cryotan Breath
-High Pressure Fluid
-Abyssal Pressure
-Thalassa's Chosen/Ocean Rain
Runes and Mutant Runes are the same as above.

Build Explanation:
With Cryotan Breath, Thalassa's power reaches a whole new height, by being able to deny enemies for 2 turns instead of 1. Thalassa's Chosen has way more merit here as well, since the Freeze Hater buff will be effective thanks to Mega Freeze being counted as Freeze and lasting 2 turns, meaning the target can do way more damage for a longer time.

Rank2: Thalassa learns "Waves Momentum" at this level, a single target buff removal followed by Mega Freeze.
Moves:
-Cryotan Breath
-High Pressure Fluid
-Waves Momentum
-Thalassa's Chosen/Ocean Rain
Runes and Mutant Runes are the same as above.

Build Explanation:
Same build, but Abyssal Pressure is replaced by Waves Momentum, since the buff removal effect is more valuable than AOE damage.

Rank3: Thalassa learns "Plankton Eater" at this level, a single target trait disable that gives an extra turn to Thalassa.
Moves:
-Cryotan Breath
-High Pressure Fluid
-Plankton Eater
-Thalassa's Chosen
Runes and Mutant Runes are the same as above.

Build Explanation:
Plankton Eater is one of Thalassa's most crucial attacks. This allows her to counter opposing Thalassa, since by disabling her trait, you remove the Freeze immunity of all enemies. In addition, this move gives her the edge against Anticipation monsters, since the trait disable comes before the extra turn, preventing Anticipation from triggering: this allows Thalassa to safely use her other extra turn moves. Something to note here is Thalassa's extra turn CDs: High Pressure Fluid's is 2, Thalassa's Chosen's is 2, and Plankton Eater's is 4. This means that, by starting with either one of the 2 CD moves, followed by Plankton Eater and the other 2 CD move (in any order), Thalassa can use the first 2 CD move she used once more. An example is as follows:
Thalassa's Chosen - High Pressure Fluid - Plankton Eater - Thalassa's Chosen
The given order allows Thalassa to give her other 2 allies Freeze Hater and remove their debuffs. This can be very useful, or even game ending, if used in the right situation. Don't worry about Stamina costs, since her trait will result in the first 3 turns not draining any Stamina. To use this chain of moves, Ocean Rain is no longer an option.

Rank4: Thalassa learns "Abyss Bottom" at this level, a single target buff removal, followed by a single target trait disable, followed by an AOE Mega Freeze.
Moves:
-Abyss Bottom
-High Pressure Fluid
-Plankton Eater
-Thalassa's Chosen
Runes and Mutant Runes are the same as above.

Build Explanation:
Abyss Bottom is arguably the most powerful deny attack in the game as of the time of writing. It is one of the very few moves that completely ignores Mega Taunt SCs, as it removes buffs before applying the Mega Freeze, and is initially single target. It can also be combined with High Pressure Fluid and Plankton Eater to Trait Disable multiple enemies and remove their buffs, resulting in one of the most devastating deny turns in Monster Legends. The last move is still Thalassa's Chosen for the extra turn shenanigans you can pull. For example,
High Pressure Fluid - Plankton Eater - Thalassa's Chosen - High Pressure Fluid - Abyss Bottom
The given attack order allows Thalassa to, theoretically, remove the buffs of every single monster on the enemy team and remove the traits of 2 enemies before applying an AOE Mega Freeze, leaving just the landing of the attacks the only obstacle before her.

Teammate Options: The double Stamina portion of Thalassa's trait can be used in many ways; a few examples include Cryotan without Stamina Runes to use Boösaule Montes without sacrificing Life, greatly increasing the power of extra turn spammers and Stamina restoring moves restoring double the amount they're supposed to. For more Teammate options, check out this article.

Countering Warmaster Thalassa: How do you counter the best monster in the game? By using the best monster in the game. Thalassa is a very solid counter to... herself, since she gives her team Freeze Immunity. Whichever Thalassa outspeeds and uses Plankton Eater or Abyss Bottom wins this battle, and you can give Thalassa faster allies like Warmaster Sherezar or Countess Flawless to stop the opposing Thalassa from doing this. Another important tool against Thalassa is Anticipation, but it will need to be paired up with a (Mega) Taunter: a vicious Thalassa counter is the duo of Dunn Ra and Hookuai; Thalassa needs to get rid of Dunn Ra's Mega Taunt to touch her team, but if she uses High Pressure Fluid, she will give Hookuai the turn, who will activate her CDs, which bypasses Tough. If she uses Abyss Bottom instead, Hookuai won't get Frozen and the other ally will do the calculation with their trait still active, and they can dodge it if they have a Hardened variant. For more Counter options, check out this article.