I just can't imagine that Rhyas with only Critical Decap and PS 13 and fury 5 has enough oomph to reliably assassinate. Hordes casters will just transfer away the one critical, and as rule it's pretty unreliable.
Against squishier casters, for sure, but that feels like a pretty limited game plan and not a very flexible "drop". To me you would want to be about to always THREATEN the assassin run while still enabling the threat of the rest of your army, which in her case is going to be melee only.
Take a look at JVMs Rhyas list from SOO. It was double Thrones and Scytheans, if I recall, which in their own have super strong assassin potential on her feat turn. Played in Oracles with BFS and Bayal to lower defenses and proc Battlewizard from the feat attacks, you've got extremely unpredictable threat angles. Then you have the icing which is Rhyas herself. I think my version of the list would look something like this:
War Room Army
Legion of Everblight - rhyas Oracles
Theme: Oracles of Annihilation
2 / 2 Free Cards 75 / 75 Army
Rhyas, Sigil of Everblight - WB: +30
- Zuriel - PC: 18 (Battlegroup Points Used: 18)
- Scythean - PC: 16 (Battlegroup Points Used: 12)
- Seraph - PC: 14
Throne of Everblight - PC: 16
Beast Mistress - PC: 0
- Shredder - PC: 4
- Shredder - PC: 4
Blighted Nyss Shepherd - PC: 1
Blighted Nyss Shepherd - PC: 1
Blackfrost Shard - Sevryn, Rhylyss & Vysarr: 9
Blighted Nyss Hex Hunters - Leader & 9 Grunts: 15
- Bayal, Hound of Everblight - PC: 0
Ice Witches - Leader & 2 Grunts: 7
THEME: Oracles of Annihilation
You end up with a crazy amount of unpredictable threat angles. Hex Hunters Shadow Binding and Hex Blasting everything, Ice Witches for Puppet Master, even the Mistress and Shredders enjoying their additional attack and placement for fun Flank antics.
If you can get a Murderous Rapport Scythean anywhere near their caster... *shudder*