D&D 5E Rule Questions: Invoke Duplicity and Dragon's Breath

[Celtavian]

Invoke Duplicity: Does it take up the cleric's only concentration slot or is it only like concentrating on a spell, but does not take up the caster's single concentration slot?

Dragon's Breath: Is dragon's breath a magical effect? It is implied that dragons are magical creatures. They get all types of strange lair actions that seem magical. The only part of them physically that could be magical is their breath weapon.

We're having trouble defining magical effects in this game for the purpose of special abilities that provide advantage or bonuses against magical effects. How is everyone else determining what is or is not a magical effect for abilities like the gnome saving throw ability and spells like Circle of Power?

 

[Staffan]

Invoke Duplicity: Counts as a concentration spell.

Magical effects: DM's call. I would consider breath weapons magical, seeing as the amount of damage they do at higher levels is way above any natural source.

 

[Celtavian]

Received this reply from Crawford:


A monster ability is magical if it involves a spell, is a spell attack, or is described as magical (e.g., Change Shape).



If it doesn't say magical in the ability, I guess not a magical effect. Dragon breath weapons are not magical. You were right about Invoke Duplicity. Reduces the usefulness by leaps and bounds considering clerics spend their concentration slot on bless the vast majority of the time due to bless being the equivalent of a 6th or 7th level spell using a 1st level spell slot. I do still like the spell options for the trickery domain.