Simple Mana bar with 5 Second rule and mana ticks. Works with drinking, etc.
How the 5 Second Rule seems to work in classic wow:
After 5 seconds has passed and you've not done a successful cast. Then you're eligible for MP2 or (Mana ticks) which seems to be controlled by the server.
This can come at any server tick so the math is actually (5 seconds + Next Mana Tick) which could be e.g. 5 + 0.2 seconds or worst case 5 + 2 seconds. This is included in the latest update of the WA
If you only want to use the 5 Second Rule as an overlay for your casting bar then you can just remove the other auras and place the MP5 bar (5 seond rule) where you need it to be.
This is pretty much a cheap version of the 5 Second Rule addon in Classic WoW.
Mana bar layout
After Casting the 5 Second Rule kicks in and a spark starts moving towards the left. " <--- | "
After the 5 Second Rule has finished a spark starts moving from the left to the right. " | ---> "
