D&D 5E Arcane Trickster/Bladesinger - When to dip?

Irregular_Gnoll said:

When you hit Wizard 2, you want to be able to pick up 2nd level spells. Getting up to R3 for Arcane Trickster is required before you hit W2.
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You can either pick up Shadowblade at 6 and keep it as one of your AT spell slots from here on out, or you can snag it at level 5 as W2. Since we get a buff to cantrips at level 5, I postponed Shadowblade to level 6 so I could use it as an AT spell slot.

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Your spell progression is a bit off, Irregular_Gnoll. Keep in mind that while you combine your Wizard and Arcane Trickster spellcaster levels when calculating your spells slots, your spells known are decided by your levels in each class separately.

So, for example, to learn a 2nd level spell like Shadow Blade, you must be either Wizard 3 or Arcane Trickster 7. Prior to that, at something like W2/R3, you will have 2nd level spell slots that can be used for upcasting 1st level spells, but you won't have any 2nd level spells known. Nor would you be able to scribe 2nd level spells into your spellbook yet, if you were to find a 2nd level spell scroll.

In addition, even once you had access to 2nd level spells at something like W3/R3, you could only learn them as Wizard spells. You couldn't take a 2nd level spell like Shadow Blade as an AT spell at W3/R3, because you don't have any AT 2nd level spells known until R7.

Hmm I admit I was under the impression I could add a spell from the list for a level I had spell slots.

Here's the Wizard rule.

Learning Spells of 1st Level and Higher Each time you gain a wizard level, you can add two wizard spells of your choice to your spellbook for free. Each of these spells must be of a level for which you have spell slots, as shown on the Wizard table. On your adventures, you might find other spells that you can add to your spellbook (see the “Your Spellbook” sidebar).

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Here's the Arcane Trickster rule.

Whenever you gain a level in this class, you can replace one of the wizard spells you know with another spell of your choice from the wizard spell list. The new spell must be of a level for which you have spell slots, and it must be an enchantment or illusion spell, unless you’re replacing the spell you gained at 8th, 14th, or 20th level.

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I appears that you are correct regarding Wizard, but the Arcane Trickster rule seems to allow you to pick up a spell for which you have spell slots, not as according to the Arcane Trickster table, like it states in the Wizard rule.

I'll have to recalculate spell progression for the wizard, but this makes Arcane Trickster even better if they are able to add spells for which they have spell slots, while Wizard is held back a bit.

Reread the multiclass spellcasting rules. The only thing that being multiclass affects is your total spells slots. Spells known are driven by your classes individually.

So that section on the Arcane Trickster's Spells Known should be read as: "Whenever you gain a level in this class, you can replace one of the wizard spells you know (as an AT) with another spell of your choice from the wizard spell list. The new spell must be of a level for which you have spell slots (as an AT), and it must be an enchantment or illusion spell, unless you’re replacing the spell you gained at 8th, 14th, or 20th level."

You still have to follow the AT spells known chart, even as a multiclass character. You would just get to add your Wizard caster level when determining overall spell slots. You don't get to gain higher level AT spells known any earlier than a single class AT.

So even though your character as a R3/W2 has 2nd level spells slots overall, they only have 1st level spells known as an AT. Thus, if you were to level up to R4, you could swap out one 1st level AT spells for another 1st level AT spell, but you couldn't swap it out for a 2nd level spell, since you don't gain 2nd level spells as an AT until R7.

Oh man. You are 100% correct. I'll have to rebuild this entirely. Thanks for pointing out my misunderstanding before I got too far into the build.