I really like the idea of a stackable shield, and gravity shield could be the right choice, but imo upped version is OP, compared to unupped one too.
Max reduction with unupped version is 6, at the cost of 12
vs a 32 max reduction (huge) at the cost of 18
for the upped one.
Unupped version is pretty balanced, and this is my suggestion for the upped version:
- first shield reduces damage by 1;
- second shield added, reduces damage by 2;
- third shield added, reduces damage by 3 and so on, having this values: