Branded is a strong Midrange deck that has a myriad of tricks and maneuvers. It is better to not shotgun your starter against them, as Albaz can fuse with your Rex if you only drop your LP to 2000. It also enables the Bystials to banish your monsters instead of theirs. Patience is the key. If you have Ash, it is better to save it for Branded Fusion, as a single Branded Fusion resolve could net them a Mirrorjade, a Branded Beast, and a Branded Banishment, all of which can easily out your Rex.

Notable dangerous cards:

Super Polymerization

Branded Banishment

Branded Beast

Titaniklad the Ash Dragon

Labrynth is a control deck that is very effective against other control decks, and yes, that includes us. Their Big Welcome should be stopped at all costs, as it gives them a monster presence that enables Big Welcome's grave effect to easily out Rex or Regina. Their Lady being able to be triggered off our traps is also a pain. That does not stop there, most of their Trap Cards are very effective against us (Ice Dragon's Prison, Karma Cannon, Deck Devastation Virus, Dimensional Barrier).

The most effective way to deal with them is to save your Ash, Judgments, and Thunders for their starters (Welcome and Big Welcome). Use brute and Kentregina's copy effect to dismantle their backrows.

Notable dangerous cards:

Big Welcome Labrynth

Labrynth Labyrinth

Deck Devastation Virus

SHS is a combo deck that usually runs no Spell/Trap. That means you can worry less about them stealing your monster with Talent. Caution is still advised as they can run monster-based board breakers such as Kaiju or Kurikara. Their in-archetype Synchro Monsters can attack using their DEF, which is dangerous as Rex only drops their ATK.

Notable dangerous cards:

Bagooska The Terribly Tired Tapir

Superheavy Samurai Brave Masurawo

Mannadium is a combo deck that can end on a strong board with an omni-negate Counter Trap, which means our usual Frenzy + Strike + Ferret wipe will not always be reliable going second against them. They can also search Reichphobia mid-combo, which can destroy our cards. They can stall with defense positioned Vicious Astraloud, which can't be destroyed by battle. Thankfully we have Brute, Ferret, and Chaos Angel to answer that.

Notable dangerous cards:

Primitive Planet Reichphobia

Mathmech is a Cyberse deck that can net a lot of advantages just from a single Circular resolve. If we are going first, it is one of the easiest matchups, as their extra deck has no way to deal with Rexterm. You still have to be mindful of Terahertz's continuous effect, though, but it can still be handled by simply activating Rex's ATK reduction effect during the end of the main phase.

When going second, it could be rough with Superfactorial usually dismantling two of our traps, as well as negates from Desavewurm. A smart Mathmech player will chain Terahertz to your Kentregina effect when copying a starter to summon  Rex, sending Aggregator that will negate your Rex. So sometimes going straight into Rex is better.

Notable dangerous cards:

Bagooska (rarely)

Kashtira is a deck that excels in banishing and locking the enemies' zone.

Notable dangerous cards:

Scareclaw Kashtira

Red-Eyes Flare Metal Dragon

Snake-Eye is a new contender on the ladder. 

Notable dangerous cards:

Sinful Spoils of Subversion - Snake-Eye

Underworld Goddess of Closed World

Everything Mikanko does, it counters Dinomorphia.