Good point and changed. Anything else as keen to publuish as topical on twitter
I keyed it out on CR caluclator and came out as 3 - but if you feel spells make it stronger then 4 is fine
Well it's kind of at the dividing line. NPC type spellcasters tend to have CR of at least half their level in 5E, i.e.:
Mage (9th level spellcaster) CR 6 (level+3 / 2)
Druid (4th level spellcaster) CR 2 (level / 2)
Priest (5th level spellcaster) CR 2 (level-1 / 2)
The lizardmage is a 7th-level caster, which ought to put it at Challenge 3½ from the spells alone. Most of its spells are lightning or thunder, so do an additional 2d6 damage due to its
Heart of the Storm trait, which I think is worth another half-CR for 4.
Also, it's HP, AC and melee ability are noticeable better than a typical spellcaster.
By the way, did you consider having it produce frogs as a spell instead of an action? It could use a variant
conjure animals, either a 1/day
Innate Spellcasting or just added to its spell selection?
Like so:
3rd Level (3 slots): conjure animals (giant frogs only), gust of wind, shatter, warding wind
Innate Spellcasting. The lizardfolk sorcerer's spellcasting ability is Charisma. The lizardfolk can innately cast the following spell, requiring no material components:
1/day: conjure animals (giant frogs only)
That would make a couple of significant changes though.
First, it summons eight giant frogs each time instead of 2d4, as
conjure animals summons eight beasts of challenge rating 1/4 or lower.
More importantly,
conjure animals is a Concentration spell while Summon Frogs doesn't require concentration, allowing the sorceror to cast spells while its frog allies protect it.