Crimson Bat belongs in Tier 1. Very powerful AoE true damage dealer, plus double skull damage to wounded enemies when fully traited, and gains life with every cast.
On this scale, Bone Dragon belongs in tier -5 or something.
Maw is at least tier 2, Silvermaiden is not that high because she doesn’t actually do anything dangerous. Krystenax may be tier 1.
It would be easier to quantify a bunch of these if it was just one rarity tier of troops, i.e. all legendaries, but of course this has been done before.
Mine would be as below - edited to add a fourth tier
Tier 1 (hardest troop to beat):
Bone Dragon
Tier 2 (troops that can cause big problems):
Wraith
Emperor Khorvash
Queen Mab
Mercy
The Great Maw
Kerberos
Kraken
Forest Guardian
Tier 3 (troops that can cause big problems but are less likely to cause you to lose the game):
Sheggra
Infernal King
Crimson Bat
The Dragon Soul
Krystennax
Gorgotha
Manticore
Spirit Fox
Tier 4: (troops that aren’t dangerous on their own, but if used well can lead to some game changing damage):
Valkyrie
Giant Spider
Apothecary
Hellcat
Alchemist
Green seer
Deep borer
Lady Anariel
Venoxia