The Alien Heroes are a group of heroes that can be summoned through a ritual from omnitrixes created by Azmuth to help the cardinal heroes fight against the waves of catastrophe. 

The omnitrixes allow them to transform into aliens like Ben Tennyson and have Ace Aliens. Ace Aliens are the aliens that represent the type of hero they are and can remain in that said alien form for as long as they want without timing out.

The watches can absorb materials which gives the Alien Heroes access to alien forms depending on what type of material the watch absorbs. 

Like the Cardinal Heroes, the alien heroes have status magic which allows them to see their statuses and level and can grow stronger when fighting and defeating monsters.

The Alien Heroes can be with any Cardinal Hero as they do not repel any of the legendary weapons or other omnitrixes so they can level up with other heroes.

The Alien Heroes are capable of wielding any type of weapon without weapon restriction unlike the legendary weapons.

Some Omnitrixes can wait for worthy candidates and chose them to become Alien Heroes like the Vassal Weapons.

Like Cardinal Heroes, the Alien Heroes can unlock certain skills depending on how high their level is and what number of aliens they have unlocked.

The Alien Heroes' watches can scan other aliens for their DNA and unlock alien forms for them.

The Alien Heroes' watches have communication which can help them be in touch with each other even if they are separated.

The Alien Heroes' watches have a master control if they have reached the requirements for it or is unlocked by Azmuth himself.

The Alien Heroes are able to change from one alien to another like Ben 10.

There is a total of Alien Heroes as there are alien forms in the Omnitrix.

The Watches are able to choose their candidates.

Well that is it for now, I hope this will help you guys understand the alien heroes now. If any of you have any questions about the alien heroes, comment me and I will give you all the answers for those questions. Dimitron75 out. ;)