Only Immortals like Baseball

Gaster is commonly assume to be the "man who speaks in hands" Riverperson tells us to beware in Undertale, as Wing Dings, Gaster's font, uses many hands in it's typeface

Riverperson also warns against a "man who came from another world", this could be about Gaster again, though many believe they are referring to Sans with this one

(Sans is tied back to Gaster with his use of Gaster Blasters and the Aster typeface)

The Mystery Man sprite is very commonly assigned to Gaster, this sprite can be found in a room between two rooms in Waterfall through random chance, much like the Egg Rooms in Deltarune

"There is a Man here" - spr_mysteryMan - spr_riverMan

The River Person says whether they are a Riverman or woman doesn't really matter

Kris is Non-binary

"Egg" is a common way to refer to a Transgender person who has yet to realize or accept they are Transgender

An Egg is also a child or offspring (usually)

In Deltarune on Playstation the only way to avoid the "Complete Without Issue" achievement at the end of every chapter is to acquire this Chapter's egg

Getting no achievements by the end of Chapter 4 will cause Gaster (assumed) to comment that you have achieved nothing, this could imply he is the one giving out the achievements himself

This could then imply Gaster and the Egg Man are at Odds in some way, as he sees acquiring the Egg as an Issue

Issue also has a double meaning, in genealogy it is used to refer to a person's decedents

Roots has a similar double meaning, literal Roots of a plant (like a Tree), and familial or cultural origins

The songs Digital Roots from Chapter 2 and Bit Roots from Chapter 3 both play in areas where Friend can be found

In Chapter 3 Friend is summoned by The Nightmare Boss (Eram), in mmorpgs smaller enemies summoned by a boss are typically called Ads

(I've also always felt the bombs from Chapter 3's8-bit minigames look like eggs. Also Nightmare's animation of throwing said bombs also gives Egg but I can't explain that one it's a vibe thing)

All armor related to Spamton resist both Puppet and Cat attacks

In a Spamton Sweepstakes tweet Spamton refers to Puppet and Cat as an Elemental Pair

Friend being summoned by The Nightmare Boss could imply Friend is being controlled by it, or working for it, a puppet like Spamton and Kris, this why Cat and Puppet attacks are a Pair

(Catti and Jockington are always partners Catti is a Cat so is Jockington a Puppet???)

(The Tail of a cat is just a snake is disguise Temmie Tweet)

(Pluey's tail has a mouth????? LIKE JOCKINGTON????)

Spamton gave Noelle a Pipis as a [CHARITY] for her reading his emails. This caused her to have to delete all her pets in her copy of Cat Petterz

A strange egg that never hatched appeared in Noelle's Cat Petterz. She took care of it until it eventually "Left Due to Happiness"

Noelle describes Cat Petterz's art style as unique as all the cats are made of individual circles making up the cat's body

The "Tail of Hell" image in the prophecy is a collection of circles in a vague serpentine line

(in the same room as the Tail of Hell panel you can find the Jockington Grows the Beard prophecy hidden)

(the Organikk with this panel says; "Before the clock strikes midnight the shadow will grow! O, the shadow will grow, serpentine! Even when the clock ran back, the shadow was growing! A patch of shadow, slithering on, slithering on, serpentine!)

Catti and Kris studied and practiced the occult together as kids, and are even rumored to have attempted to summon a demon together

(CATTI AND JOCKINGTON ARE ALWAYS PARTNERS-)

The Tail of Hell could be connect to "Lost where the forest would grow the children followed the Pointed Tail. The poor children!"

The Organikk who says this says they heard it somewhere in between, and is located in the egg room of the chapter

Spamton first brings up Mike after being asked about Friends in his shop dialogue. Despite claiming not to need him, Spamton also calls out to ask if Mike is watching when defeated with violence

The Real Mike supposedly warned Tenna against forcing (in Tenna's own guilt blinded words) Spamton to sign a contract, claiming the he COULDN'T sign it, and that something bad would happen if he did

Mike genuinely seemed to care about Spamton and possibly Tenna as well and seemed to want them to be happy, even if logistically a CRT Television and a Spam Email should not be a Darkner Pair

This could imply Mike and Spamton's mysterious Benefactor then are in Opposition, as they cut Spamton off from his support when he offered to share how he got "big" with Tenna

While we don't know what exactly Spamton's Phone Benefactor told him, they are implied to be the same "strange someone" who found and spoke to Jevil, causing him to begin to change

We can assume then the Benefactor knows the world of Deltarune is a Video Game, as that's implied to be what they told Jevil and Spamton, rather than just the Prophecy

The second Blue Addison standing outside of Spamton's shop after finishing the Neo Boss fight says the noise coming from Spamton's phone left hanging in Queen's mansion sounded like "Garbage Noise"

Attempting to use Kris' phone in any dark world will result in the text "It's nothing but Garbage Noise" after an unskippable moment of playing the sound effect mus_smile.ogg

This sound effect also plays slowed and quieted around the bunker and in the Holiday House basement

It also plays during Entry 17 in Undertale, our first connection to W.D. Gaster

The first appearance of Friend happens in Spamton's basement and is categorized similarly as objects used in the Goner Maker (DEVICE_FRIEND and IMAGE_FRIEND), nothing else in the game is categorized this way

And that's all I have. I'm pretty sure. And again I don't know what this all might mean. Other than that Gaster has a lot of Haters in-universe.

I'm sure there's better, more organized collections of all this exact information, but I needed to do something with my snail infused brain tonight, and that something turned out to be trying to figure out Who the HELL all these Men are, or at least get all my knowledge about them written down.