To evolve a hero you need to power up your hero to become +5. Their level are also need to be 30.
For power up guide, visit THIS PAGE.
Fixed evolution will give you the same hero from previous tier, with higher status. This will allow your favorite hero can be used on harder difficulty.
For Random, it’s completely random. So you may get a bad hero from higher tier (such as 5 stars lang). However you don’t need to worry because if you don’t like that hero you can use it to create higher tier later. For bad 6 star heroes you simply use them for awakening material.
No, fixed evolution has few drawbacks (disadvantages), they are
Many lower tier heroes (1- 4 stars) don’t have “full” skills and traits. Only 5 stars heroes (and above) who have 3 traits.
If you have 3 star heroes with normal base attack 1000. You fixed evolution this hero to become 4 stars, and at level 30 it has 1200 attack. Each power up should give you +120 attack, however because the original value of this hero are 1000, it only get +100 attack instead of +120. In the beginning it may seems not that important, but the difference will become really big, especially if you do the fixed evolution on 3 star heroes (and below).
Note: I am not sure if the power up rule also affect the legendary heroes, as they start at 4 stars and you need to do the fixed evolution to make them into 6 stars.
Nope, the fixed evolution is really useful if used on right hero. Other than that I really recommend you to use random evolution. Evolve 2 3 stars heroes with random evolution can also gives you legendary heroes (the chance is extremely small though).
A hero with Excellent Trait: If the hero has a trait that can affect the entire party, then it’s probably worth for the fixed evolution process. However, you usually need to awaken that hero to make that trait affect your entire party. Example: Miho (4 stars), Captain Radin (5 stars), etc.
I will list all my recommendation for fixed evolution on the main page of wonder tactics guide, so please check it later on the section called “best 3/4/5/6 stars heroes” (the pages are still under construction).
I think that’s all you need to know about fixed and random evolution, feel free to ask me in the comment if you have questions and suggestions for other tips.