Her abilities are always relevant and if her ultimate occurs then she completely decimates someone's board position
Vivi Ornitier, of course, is seen as the tripartite flagbearer of the split Izzet builds, as it is considered one of the key cards that will keep the color combination still alive and fighting in post June 2025 Standard meta
The ward cost is harsh and amass for every opponent's spell really adds up
As long as you can put Blight counters on your creatures, you can do all sorts of things: raising the dead, drawing cards, dealing damage, gaining life
Honestly, I'm fine paying the full cost for her most of the time
Astrologians Planisphere, Summon: Knights of Round and Yuna, Hope of Spira have all fallen under this category