I'm currently working on my version of FE4 with these changes:
1. Enemies drop half gold when defeated without steal skill.
2. "Sigurd" and "Ethlyn" are now twin brothers and they have minor light blood and they're paternal half-brother of "Diadora". The two of them, along with a tactician with minor darkness blood have a fixed child and forced marriage (Awakening style without maiden), meaning that they always have 3 children, 2 from their wives.
3. There are 16 different blood types: 3 swords, 2 lances, 2 axes, 2 bows, 1 staff, 1 fire, 1 ice, 1 thunder, 1 wind, 1 light, 1 darkness. Some of the blood's bonuses are different than FE4 to make more sense. There are 15 crusaders in this version.
4. There are way more magic users, including glass cannon wizard/witch.
5. "Jamke" and his family has minor bow blood, different than "Brigit" and "Edain"'s. They're distant relatives since the said crusaders are siblings.
6. Silesse was founded by wind and lance crusader.
7. Most classes are unisex, including White Knight (Troubadour), Sky Knight, Fighter, Mercenary, Alchemist, Spy, Outlaw, and Magic Knight.
8. Darkness blood-bearers are allowed to have multiple children, but they're quite infertile in general, but still not allowed to marry fellow darkness blood-bearers.
9. Each generation has 35 playable characters.
10. "Azelle" and "Lewyn" aren't the only playable blood bearer of their own element. "Azelle" has a twin brother while "Lewyn" has cousin.
11. "Claude"'s sister is alive in mine, but lost during childhood. She appears to marry the tactician's brother under the dark lord's control.
12. Dragon knight's main weapon is axe and they can use lance after promotion.
13. Sky knight, mercenary, and fighter have different weapon types depending on their gender, also applies to their promotions. This is especially true for sky knights since male promotes to dark fliers while females promote to falcon knights.
14. The magicians have nice magic and usually nice resistance growth, making "Ethlyn", "Azelle", "Lewns", "Tailtyu", "Edain", and "Claude" much better. Priests are now tanky and can equip light instead of anima upon promotion.
15. There is a warrior queendom, consisting of mostly amazons at its capital.
16. "Lex" is now dragon knight while "Shannan" is wanderer.
17. The only substitute children with crusader's blood are the amazon's children's because their cousins take their places just in case. Both have minor axe.
18. Staff range is now 1-2 in general. Long-ranged heal is available. Some of them have their rank altered.
19. Master knights can only equip sword, lance, axe, bow, and staff. It's female-only now.
20. Renewal is now unique to light crusader's descendants.
and many more! It's too much to post here all at once 😄