For a Hollow to transform, you need consumes! Not kills! To check how many consumes you have, look in the server tab.
Small Hollow = 400-500 consumes
Medium Hollow = 900-1000 consumes
Large Hollow = 1400-1500 consumes
Menos Grande = 2000 consumes
Adjuchas = 3000 consumes
Vasto Lorde = 6500 consumes
