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The Bone Devil, when using the Devil Summoning Variant, has the ability to attempt to Summon Devil (1/Day).
Having a read through the appropriate page on themonstersknow.com it discusses the idea that it makes the most sense to attempt this on turn 1.
This means we have a scenario were the Bone Devil succeeds on the summoning and now has (on average) 7 spined devils fighting with them.
How does this effect the encounter difficulty? Is it as simple as going from a 5,000 XP encounter to a 8,150 XP encounter (adjusted 16,300)?
The CR level given to the Bone Devil, does this include this scenario or is it seperate?