UPDATE: Doesnt work as expected - dont use yet.
Extra Boss HEALTHBAR with marks at PHASE change percentages.
Text and audio WARNINGS at 80%, 60% and 30% FOR MORE AWARENESS OF UPCOMING PHASECHANGE AND SHATTER.
https://www.wowhead.com/spell=351066/shatter
Requirements:
https://www.curseforge.com/wow/addons/sharedmedia_dnnsgt for the audio warning. (audio warnings currently say "HEAL CD!" in german)