There are little boxes in Borderlands 3 with the Gearbox logo on them.

Threshers aren't native to Kairos. They migrated from Elpis through a meteorite, and you can find the impact crater in the Stoneblood Forest section of the map.

The Gearbox Logo can be spotted on a christmas bauble in the opening cutscene for Borderlands 4s Mercenary Day DLC.

Amon is the only one who pushes the button during the cutscene at the end of BL4s Mercenary Day DLC with his fist.

The disco balls that appear after finishing the PowerDrop gambling side quest in the Fadefields, use the Phosphene rainbow glow effect and have unique turquoise colored loot beams. (Borderlands 4)

When Rush sacrifices himself during Borderlands 4s Story Mission "Rush The Gate", he doesn't disappear. Instead he simply turns invisible and any interaction option for him is disabled. You can still hit him with your vehicle though.

Many barrels that you encounter throughout Borderlands 4 don't have the Outline Shader applied to them.

You can find the wreckage of Raum-Kampfjet Mark V (RK5) from Borderlands: The Pre-Sequel in Borderlands 4 on Elpis.

Update: The date has been removed. It's replaced with what seems to be the games version number.

A couple of Order fences do not have the outline shader applied to them.

In Borderlands 4, in the bottom left corner of the Pause Menu, you can find the date April 28th, 2019 (4282019). On that day Joshua Davidson (Senior Sound Designer from Gearbox Software) announced that Borderlands 3 would have 7500 unique weapon sounds.

Crazy Earl is just a floating head. In Borderlands The Pre-Sequel in particular his neck and back of head is oddly curved/stylized.

Snack carts in Borderlands 3 have napkins with the Gearbox logo on them.

The gadgets from Lost Legion soldiers in Borderlands: The Pre-Sequel look like the soldiers gun barrel. Credit: Cocowhale

In Borderlands: The Pre-Sequel Claptrap has what looks like a bolt screwed into his head. This change is exclusive to The Pre-Sequel.

The portal from which the train in Borderlands 3's Fustercluck DLC comes out, leads to Southpaw Steam and Power, a location from Borderlands 2.

With the help of a bug when driving a vehicle, you can drastically change the feel of driving in Borderlands 3 by offsetting the camera within the Photomode.

Low Poly Wick and Warty

"Impact" is NOT the "Borderlands Font". The Borderlands font is called "Compacta Bold".

The full size of the Son of Crawmerax (with Zer0 for reference)

The tongues of Saurians are spiked and have two claws.

The entire bossfight against The Rampager is an easter egg referencing the 1986 arcade game "Rampage", in which you play as a Gorilla, a Wolf, or a dragon-like Reptile. Each phase of The Rampager represents a different character of the game. Gorilla, Wolf, Reptile (Dragon).

The Wendigo of Borderlands 3 refers to the mythological man-eating creature of the same name.

Tiny Tinas Wonderlands has a side quest that breaks the fourth wall and shows elements of the Unreal Game Engine that developers of the game were working with.

Mr. Torgue has brown eyes.

A reference to E. L. James' novel "Fifty Shades of Grey" can be found at various places in Borderlands 3.

There's a time and place for everything on Pandora.

Low Poly Lorelei (Borderlands 3)

Claptrap is (unintentionally?) dabbing when he gets pulled into the big magnet of Borderlands 3's intro mission.

There is a little wood kart on one of the roofs in Vestige (Bounty of Blood DLC, Borderlands 3)

Bandits that are mounting the Bandit Technical turret have their right foot clip through the vehicle occasionally.

Low Poly Maya (Borderlands 3)

The Gearbox logo as well as a Nyan Cat reference can be spotted on all Quick Change stations in Borderlands 2.

There is a beverage in Borderlands 2 called Clitz.

Jimbo Hodunk has a bandit head inside his head.

Low Poly Lilith (Borderlands 3)

Low Poly Hammerlock (Borderlands 3)

Weathervanes feature a Claptrap chicken in Borderlands 2.

Pandoras moon Elpis is transparent.

The train wagons for the "The Pretty Good Train Robbery" side mission in Tundra Express are stored behind rocks. Mordecai could theoretically see the corner from one of them.

Full size of the Leviathan boss in Borderlands 2's Captain Scarlet DLC. (with Zer0 for scale)

Shooting Killavolt in the nuts rewards you with the unique "DICKED!" critical text.

The weapons trinket of The Warrior in Borderlands 3 comes with 4 legs despite the Warrior having six of them. Bonus fact you might have missed: Yes, The Warrior has 6 legs.

During Troys bossfight in Borderlands 3, you can sometimes see parts of his face poking out.

The head of Super Badass Loaders in Borderlands 2 is not centered to the body.

There is a plate floating far outside of Concordia in Borderlands The Pre-Sequel.

Low Poly Wainwright (Borderlands 3)

Mortar has no head, only a face.

The lamps from the Mercenary Day DLC in Borderlands 2 don't have the outline shader applied to them.

The fish that Tannis was riding on in Borderlands is called Splorghuld the Flesh-Slayer. It died sometime after the events of Borderlands 1 and has since then been used as an exhibition in The World Of Curiosities.