Any Higher Evolutionary Form will have higher forms of intelligence, strength, speed, durability, energy projection, fighting skills, special attacks, and flavor. They are incredibly difficult, if not impossible, to kill and they certainly know it. If you know of any version higher, then that, by default is actually the Higher Evolutionary Form and who know what you're even looking at.
Technically, the highest evolutionary being is the one from furthest in the future, since almost everything is constantly evolving toward a state of most Awesome (the very definition of evolution). However, rare occasions result in certain creatures that remain static or only get more tame-ass and lame over time. These include such pitiful excuses for beings such as negative worms, the Moon Emperors, the Greek gods, reverse time beings, dinosaurs *by turning into birds, and whatever Donald Trump is. These things only get worse. However, the best possible evolutionary form of a species may be at a random point of that species short existence, and thus would need to be accessed via Time-Fuckery. Luckily (or unluckily), many of the Highest Evolutionary Forms learn how to travel through time and space. However, since time is an illusion anyway, none of this even matters.
The Highest Evolutionary Form will never be taken out by any lower member of its own order, but can and most likely will be taken out by its own hubris. Also the apex super-predator of any Evolutionary Form will be indomitable to all others. These are only superceded by the Highest of Evolutionarys, those ascended to take on the very God of all creation. The God of all creation is itself the Evolutionaryiest most High on highest. Any High or Higher or Highest Evolutionaries will eventually be defeated by Batman.
Every million years in a species' existence it will suddenly mutate to its next highest evolutionary level, having collected another million years' worth of collective biological experience. This is how evolution works, people.