2. Each base stat of the evolution except for Speed must be at least equal to the corresponding stat of its immediate pre-evo.
Some Pokemon do lose another stat other than
Speed when they evolve:
Shelgon -> Salamence,
Defense -20.
Metapod -> Buttefree,
Defense -5.
Kakuna -> Beedrill,
Defense -10.
Silcoon -> Beautifly,
Defense -5.
Trapinch -> Vibrava,
Attack -30.
Of course, all of these have distinct features, such as an evolved Pokemon coming out of a shell, loses defense but gains other stats, or loses a distinct form of offense, such as Trapinch's huge mouth doesn't get passed to Vibrava.
Here's also a few more things that I think you should mention:
1) All of any new
Eevee evolutions MUST be mono-type, and it MUST not already exist.
2) All of any new
Eevee evolutoins MUST have one stat at 130, one stat at 110, one stat at 95, one stat at 60 and two stats at 65. All of the 7 existing Eeveelutions follow that rule. They also cannot be combined exactly the same way with any of the existing Eeveelutions.
3) Some Pokemon shouldn't be able to evolve, such as: Unown, Spiritomb, Rotom, Ditto, or any legendaries. That's just a few examples.
Again, those 3 are just suggestions.
Edit: Deleted suggestion four for partner rule, and deleted Lucario out of 3.