Hello everyone and welcome to my 278th analysis, this time featuring Thundeer.
Overview: Thundeer is a very fast denier that has many deny methods under his belt, like CD Activation, random deny effects and Precision modifiers. This allows him to deny many different kinds of monsters. Most of his skills apply Shock to enemies as well, which can annoy enemies, and even break some monsters down. Thundeer eventually gets Dodge Area as well, which brings his power level to a whole new height. He has other useful debuffs like Trait Disable too, which makes Thundeer a reliable, fast and versatile denier that can adapt to many situations - these are, of course, if you rank him up. Thundeer's lack of the ability to help his teammates when they're afflicted with status effects is a pain, but it doesn't matter because Thundeer is an exceptionally powerful denier.

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.

Rank 0
Moves:
-Always On Time
-Finished Project/Watch This Movie
-Loves Spontaneity
-Don't Cross The Gifts
Runes: 3 Speed
Mutant Rune options: Speed&Life
Relics: Staves

Build Explanation:
Always On Time is Thundeer's AOE deny move that applies CD Activation to all enemies, but also applies Daze to them, which is significant because attackers tend to have 0 CD moves to combat CD Activation, and attackers hate being Dazed. Watch This Movie is a single target deny move that is one of Thundeer's few single target attacks that deal direct damage, and it applies a random deny effect + Shock to its target. Finished Project instead is a single target version of Always On Time that applies Blind instead of Daze. It's stronger against Hardened variants or monsters with immunity to certain or all deny effects, but it prevents Thundeer from currently being able to beat Dodge Area monsters one on one. Loves Spontaneity is a handy extra turn move that can rid Thundeer of Total Blind or shorten the lifespan of other annoying debuffs, while also giving your team a handy Damage Boost without losing any momentum. Lastly, Don't Cross The Gifts applies Daze and Blind to all enemies, which makes them very unlikely to land attacks for 2 turns, while also giving them Shock to prevent extra turn moves from shortening this time. It can handle enemies that cheat Always On Time, plus not many monsters are immune to Blind or Daze.
3 Speed with Life Mutations is a standard on deniers.

Rank 1: Thundeer learns "Stolen Christmas" at this level, a move that gives Thundeer True Vision and an extra turn. His Trait also evolves to include a 50% Life increase for the team.
Despite this being better for Thundeer himself, Loves Spontaneity also serves as an extra turn attack, but it has much more use in giving the team Damage Boost.
The Trait Evolution helps against attackers, and it's especially amazing in Taunt - Dodge Area cores to make the Taunt monster more durable, a core Thundeer will find himself in in a couple of Ranks.

Rank 2: Thundeer learns "The Fastest Claus" at this level, an unresisted single target Base 25 move that applies Trait Disable to its target, then removes its buffs, then gives Thundeer an extra turn.
Moves:
-Always On Time
-The Fastest Claus
-Loves Spontaneity/Finished Project/Watch This Movie
-Don't Cross The Gifts
Runes and Mutant Runes are the same as given above.

Build Explanation:
The Fastest Claus is a godsend for Thundeer, allowing him to break Taunt - Dodge Area cores, eliminate Anticipation monsters, remove Evasion or Dodge Area from its target, and so much more, without losing momentum. It also counters monsters with Positive Effect Protection traits such as Neobuki, though it sacrifices the ability to Trait Disable monsters with Evasion. Still, very few deniers can claim to do this kind of thing, and the ones that can are extremely powerful ones, like Warmaster Thalassa. Since this is an extra turn move, Finished Project or Watch This Movie can replace Loves Spontaneity if you find them more valuable than another extra turn move + AOE Damage Boost.

Rank 3: Thundeer learns "Christmas With The Deers" at this level, an unresisted single target Base 30 move that activates the CDs of its target, then gives Thundeer an extra turn. His Trait also evolves to include a SC: Dodge Area.
Moves:
-Always On Time
-The Fastest Claus
-Christmas With The Deers
-Don't Cross The Gifts
Runes and Mutant Runes are the same as given above.

Build Explanation:
Christmas With The Deers combines the best aspects of Thundeer's 3rd slot options at Rank 2: it gives him an extra turn like Loves Spontaneity, it is a CD Activation like Finished Project, and it does damage like Watch This Movie. For this reason, it is the definite choice for the slot, while also giving him a single target deny move.
The Trait Evolution is extremely significant, since monsters with Dodge Area are very strong in the current meta thanks to their insane utility, and their ability to form the formidable Taunt - Dodge Area core, the most used core by high level players.

Rank 4: Thundeer learns "Thundeer Skellington" at this level, a Thunder Base 25 AOE that applies a random Mega deny effect and Shock to all enemies.
Moves:
-Always On Time
-The Fastest Claus
-Christmas With The Deers
-Thundeer Skellington
Runes and Mutant Runes are the same as given above.

Build Explanation:
This is the first move in the game to apply random Mega deny effects, which makes it a bit unpredictable against some enemies, but very strong in general since it's intended to be an AOE that denies enemies for 2 turns. It replaces Don't Cross The Gifts since it's much more powerful, plus Always On Time already applies Daze to all enemies, and while that's not as strong as Daze + Blind, it's more than worth it to pick up Thundeer Skellington over an extra Blind.

At Rank 5, Thundeer's Trait evolves to include a SC: Random Negative Effect.
This is not necessary or strong, but it can help at times. Also, it's not a minus, so there's nothing wrong here.

Teammate Options: The Fastest Claus alone makes Thundeer very desirable for any team. Beyond Rank 3, Thundeer can be an exceptionally powerful member of Taunt - Dodge Area cores, since he can ruin opponents that are running the same strategy, plus the Life increase makes your Taunt monster much more durable. For more Teammate options, check out this article.

Countering Thundeer: Thundeer has no way to remove debuffs, save for one very underwhelming move which most players won't run, so try applying debuffs to his team because he can't get rid of them - also note that Torture effects don't care about the Life Increase since they do damage based on maximum Life. Ugluk and Hookuai are very effective answers that can fend off both deny effects and CD Activation. For more Counter options, check out this article.