Behold! Tem finally has a ref sheet to show off what he looks like throughout his evolutions.
Created as a villain for a friend's pokemon mystery dungeon inspired TTRPG game, he kinda came into a life of his own through a few RPs and wound up turning into a character I really really like.
As for why he's got five forms, this is basically his trajectory from that campaign. Starting out as a genetic experiment by Team Galaxy to try and create the perfect pokemon, they fused Eevee DNA and Ditto DNA with the aim to have a pokemon that could replicate any move or typing it encountered.

Thus Tem was created, his second form is what he looks like after replicating all the possible types, and it's at this point he kinda goes rogue from his creators. Escaping and setting out on a quest to liberate himself as well as his "brothers and sisters" from Team Galaxy (Although later on he extends this goal to liberating all Pokemon from trainers and battling.)

The idea was a villain who had a noble goal, but was ultimately corrupted by power and believed that any action was worth it to secure his noble goal.
Thanks to a lucky Nat20, he actually won at the end of the campaign, defeating the party and absorbing a defeated Arceus to ascend to godhood.
From there, the epilogue was given as he rewrote and remade the world in his image, destroying gyms, freeing Pokemon and ultimately proving that he would eventually complete his goal.
The final thing the party was told was how Tem selected a few other Eevees and the only other success Project Storm (Team Galaxy's program that created him) to found a new pantheon of gods to rule the world and try to create a Utopia.

That Pantheon being
Thalassa/Bay (Vaporeon) - Goddess of the Seas
Squal (Jolteon) - God of Storms and Weather, the only other success of Project Storm
Solaria (Flareon) - Goddess of the Sun
Oniria (Espeon) - Goddess of dreams and knowledge
Nox (Umbreon) - Goddess of Night and the moon
Gaia/Leafy (Leafeon) - Goddess of Nature and fertility
Lumi (Glaceon) - God of winter
Silver Rose (Sylveon) - Goddess of love
Tempest (Eevee) - God/King of the gods

Expect art of the others eventually, cause I've got a dual form design in mind for about half of them, ranging from a hundreds of metres long sea serpent Vaporeon, to an Umbreon that is partly made out of the night sky.

Would anyone be interested in reading some stories involving adventures in his setting post-Tem ascendance or maybe a story based on the campaign itself?