What effects can modify mana abilities and be affected by Mana Relfection and Nyxbloom Ancient?
Mana Reflection and Nyxbloom Ancient are the only cards that increase the amount of mana produced by other mana abilities. Some cards decrease the amount of mana produced.

In order for one card to modify the result of an ability on another card, it would need to use a replacement effect, which would contain the word "instead". So, we can look for cards with this effect by searching for cards with the words "mana", "produce", and "instead". Of the cards we find there, only Mana Reflection and Nyxbloom Ancient increase the amount of mana produced, and Contamination and Damping Sphere decrease the amount of mana produced, and change its type.