If Pillars were to appear in Dragon Gamer since Star Swirl is the creator of Eden, what would they be like in the fic.

I would say they would be colleague of Micro Software who went separate ways to pursue their careers but years later, they're reunited and made their own game avatars to help Spike and the girls to rescue Micro from Grogar even though they are old geezers.

Rockhoof

He is a Scottish immigrant who joins police force but at some point, he suffered a career-ending injury and was retired. He ends up becoming a history teacher at college.

Mistmane

She used to be a model until an accident cause her to lose her beauty but despite that, she was glad to save her best friend, Sable Spirit and she pursues the career of landscaper.

Flash Magnus

An air force pilot who disobeys his superior to save his comrade from terrorists and ends up earing respects from his superior and others. Even though he got older, he is still respected by air forces and was promoted to be drill sergeant for younger cadets.

Somnambula

An explorer who saves an Egyptian prince and the village from a ruthless female warlord, she's retiring from her day of explorers to become motivational speaker.

Mage Meadowbrook

A doctor who is responsible for making cures for any disease and is good friends with Zecora and when she got older, she owns her own medical company and in contrast Chrysalis' corrupt medical company, Meadowbrook's company are more caring about people's health.

That's all I got for them.

As for Stygian, I would say not only he wasn't successful compare to them but he ends up creating Pony of Shadows virus to take his anger on Micro Software and sabotage Eden.

I would say that the Pillars could be special NPCs that were created by Micro Software and their purpose is to safeguard special items that could help defeat Grogar. Each of the Rainbooms try to fight the Pillars and gain special items.

Rockhoof
Opponent: Applejack
Item: Rockhoof’s shovel which can increase strength.

Mistmane
Opponent: Rarity
Item: A special flower which improves magical power

Flash Magnus
Opponent: Rainbow Dash
Item: Flash’s shield which increases defense

Mage Meadowbrook
Opponent: Fluttershy
Item: Mage’s mask which increases healing

Somnambula
Opponent: Pinkie Pie
Item: A blindfold that improves agility

Stygian
Opponent: Sunset Shimmer
Item: A shadow cloak that enhances power or something like that.

Here is what could happen if Twilight faced Star Swirl:
Star Swirl
Opponent: Twilight Sparkle
Item: A sacred textbook filled with rare spells.