I think looking back I may have mixed up the power equivalencies:
Tamas = First One (Unique Being - opposing Metatron)
Casim = Old One
Gamchicoth = Elder One
Thaumiel = Greater God
Agshekolah = Intermediate God
Golohab = Lesser God
Tagiriron = Demigod
Ghareb Tzerek = Quasi-deity
Samael = Hero-deity
Gamaliel = Template
Qemetiel = Unique Being (opposing Sandalphon) known as the Crown of Gods.
Satariel = Unique Being (opposing Adam Qadmon)
Seiriel = Prophets (followers of Satariel) known as Silent Heralds. They are giant centaur nightshades (rather than proper umbrals...even though the line is blurred between the two)
Beyond the Golohab and colossal monsters known as the Agshekolah (Breakers in Pieces). They are giant jet black cats that walk on their hind legs*. They are Anti-spirit for their ability to schism immortals. They are equal to intermediate gods in power.
*They look exactly like Tacgnol (for those familiar with that internet meme...and yes I had the Agshekolah outlined 7 years ago, long before that whole longcat business started).
Those equivalent to Greater Gods (and my personal favourite Umbrals) are the Thaumiel (Double Headed Ones). These titanic jet black monstrousities are massive humanoids with two heads, but each head hovers above the shoulders (they have no necks) and sprouting from the side of each head is one wing (pointing outwards). Entwined around each arm is a great black serpent. The Thaumiel are Anti-Time, one head attacks you in the past, the other in the future while its body attacks you in the present.
Above the Thaumiel are the Gamchicoth (Disturbers of Souls). Who 'were' the lords of the negative energy planes of Ash, Dust, Salt and Vacuum. They would sort of be semi-unique (I hadn't come up with a look for them yet but I was thinking they might correspond to various nightshade forms).
The Casim (initially named Maadim but I swopped that with the Far Realm equivalent because it was just a better fit) are great black holes acting as portals to oblivion.
Tamas is of course the first one of Entropy, but he has no real form and is the entire dimension itself. Tamas is similar to ENTROPY from the Gary Gygax novel Dance of Demons, it has no form but can weigh heavily upon other beings and objects.