With the release of Guildmaster's Guide to Ravnica, characters were given new background options. All of these options add spells to a character's spellcasting classes. One of these is the Izzet Engineer background, which allows for any spellcaster to learn and cast chaos bolt, among other spells.
The Izzet Engineer background's "Spell List" section says:
For you, the spells on the Izzet Guild Spells table are
added to the spell list of your spellcasting class. (If you are a
multiclass character with multiple spell lists, these spells are added
to all of them.)Spell Level – Spells
Cantrip: produce flame, shocking grasp
1st: chaos bolt, create or destroy water, unseen servant
[…]
The description of the chaos bolt spell says:
You hurl an undulating, warbling mass of chaotic energy at one
creature in range. Make a ranged spell attack against the target. On a
hit, the target takes 2d8 + 1d6 damage. Choose one of the d8s. The
number rolled on that die determines the attack’s damage type, as
shown below.d8 – Damage Type
1: Acid
[…]
8: ThunderIf you roll the same number on both d8s, the chaotic energy leaps from
the target to a different creature of your choice within 30 feet of
it. Make a new attack roll against the new target, and make a new
damage roll, which could cause the chaotic energy to leap again.
Combine this spell with the School of Evocation wizard's Overchannel feature:
Starting at 14th level, you can increase the power of your simpler spells. When you cast a wizard spell of 1st through 5th level that deals damage, you can deal maximum damage with that spell.
I found another question referencing wish-ing to chaos bolt. The answer references the fact that chaos bolt is not a wizard spell, and therefore the asker's desired outcome does not work. However, a key point of text from the Izzet Engineer (emphasis mine):
For you, the spells […] are added to the spell list of your spellcasting class.
This means it is now possible for a 14th-level Izzet Engineer Evocation wizard to choose to maximize the damage of a casting of chaos bolt. What happens if they do so?
Does the spell continually leap to new targets until the caster chooses no target? Since the damage is maximized, is it dealing thunder damage each time?
Am I simply too excited about this possibility? Should the 2d8 should be rolled as normal to determine damage type and leap potential, but then the spell deals 22 damage (8+8+6) regardless of the roll result?
Best Answer
Overchannel replaces the damage of the spell, not any other mechanics
The only thing that changes when you overchannel a spell is that instead of adding up the numbers on the damage dice, you use the maximum possible result. Most of the time this means there is no point to rolling the damage dice, but it doesn't say that you don't.
In Chaos Bolt's case, you'd roll damage as normal, using the type table and chaining mechanics as explained in the spell, but you'd substitute the rolled damage with maximum damage.
As an example, if you rolled 1, 2 (d8s), and 6 (d6), you would choose either acid or cold, you wouldn't jump to a new target, and you'd do 22 damage.