My understanding of multi-classing is that when one combine levels of two Full-Casters (e.g. Bard + Sorcerer) one still progresses all the way up the uniform spell slot chart to access a full suite of level 6-9 spell slots.

But if one combines Warlock levels with Full Caster levels (e.g. Bard + Warlock, or Sorcerer + Warlock) one must sacrifice the opportunity to attain both/either some amount of the highest level Mystic Arcanum 'slots' and/or some amount of the highest level spell slots.

I have to assume this opportunity cost is intentional, but is the opportunity cost of high level spell slots and/or Mystic Arcanum 'slots' justifiable from a character optimization perspective? Or would the loss of access to high level slots always make a Warlock/Full Caster mix suboptimal compared to Full Caster, a Warlock, or Full Caster/Full Caster MC?

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    \$\begingroup\$ Unless you make this more of a numbers crunch it's going to be closed because of opinion bias, because the uses of a Warlock11/Wizard9 are entirely different and unique to that of a Sorc11/Wizard9 (using this layout because thats when warlock gets their arcanum, vs other casters getting it at normal progression). Unless you want pure DPR or number of castable spells etc. this is unanswerable. \$\endgroup\$ – Nemenia May 18 '16 at 17:03
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    \$\begingroup\$ Reminder: comments are for clarifying content, not posting small or incomplete answers. Please use answer posts to submit answers instead. Prior comments containing answers have been removed, and comments correcting the prior answer-comments are appreciated and have been removed only because they're now obsolete. \$\endgroup\$ – SevenSidedDie May 18 '16 at 18:05
  • \$\begingroup\$ Per D&D design team, most campaigns peter out around level 15, meaning most characters (definitely multiclass characters) never reach the pinnacle of their powers. Should that be taken into consideration for any answers here? \$\endgroup\$ – LegendaryDude May 18 '16 at 20:43

Warlocks Have to be Different

Warlock slots recharge on short rest, so they are incompatible with other caster's slots that recharge on long rest.

That is, a full casters get more slots, but they recharge on long rest. A warlock only get 2 slots of level 5 at the max, but they recharge on a short rest, if you take 3 short rests a day that is 6 level 5 slots a day, if you get 2 short rests it's 4 slots per day... etc.

The wizard does have a special class feature that allows a 1/day ability to recharge half thier wizard level worth of slots during a short rest. But this isn't strictly the same thing as the slots recharging on any short rest, as is more akin to Warlocks capstone ability Eldritch Master. That said, the Wizard at level 20 can recharge 2 5th level spell slots or 1 9th and 1 1st level spell slot once a day during a short rest.

Slot Comparison "Even" Split - Full Caster Wins

Speaking just spell slots, it might look like it if you try to something like an even split. A Warlock 9, "Full Caster" 11 would have:

3 cantrips 
2 5th level recharge on short rest

X cantrips based on full caster class
4 first level slots that recharge on long rest
3 second level slots that recharge on long rest
3 third level slots that recharge on long rest
3 fourth level slots that recharge on long rest
2 fifth level slots that recharge on long rest
1 sixth level slots that recharge on long rest

Now, a full caster would get:

4 first level slots that recharge on long rest
3 second level slots that recharge on long rest
3 third level slots that recharge on long rest
3 fourth level slots that recharge on long rest
3 fifth level slots that recharge on long rest
2 sixth level slots that recharge on long rest
2 seventh level slots that recharge on long rest
1 eighth level slots that recharge on long rest
1 ninth level slots that recharge on long rest

Non-slot Benifits -- Boils Down to Opinions

So, what do you get for your sacrifice? - Pact Features. - Invocations. A lot of which are at-will spells that use no slots. - Pact Boons - Different spell list.

The Warlock spell list contains the Eldritch Blast, Hex, Armor of Agathys, Arms of Hadar, Hungar of Hadar which aren't on any other caster's spell lists. EB is especially powerful and is empirically the most powerful cantrip in the game (esepcially when buffed by invocations).

Granted, other casters have class features, too -- I am not down playing them. The warlock has a lot of offer for smaller "dips" for non-casters, or for primary Warlock.

3 level dip - Warlock Wins.

It wouldn't make sense for a full spell caster even split. Three levels of Warlock, however, might. A full caster would grant 2 invocations 2 cantrips (which would likely include Eldrithch Blast), Pact Boon (An improved familiar, More cantrips, or summon-able weapon), the first Pact Feature (Fey Presence, Awaken Mind or Dark ones Blessing), and 2 2nd level spells that recharge on short rest. Moreover, those 2 slots can be used with any spell you know, and doesn't have to be prepared.

At level 20, that would be at a cost of 1 5th and 1 6th level spell slot that recharge on long rest, and whatever class features you miss in the dip (Wizard, for example, would be giving up spell mastery and spell signature).

This might be worth the trade if you are a CHA based caster and want a cantrip that does 4 attacks each dealing 1d10 + CHA (+1d6 from Hex each strike) and the option of pushing the enemy back 10 feet each strike. Yes, Finger of Death (etc) can do more damage, but it costs slots.

  • \$\begingroup\$ not to be too nitpicky, but a wizard does recharge some spell slot/levels on a short rest, per the "Arcane Recovery" skill. (up to 5th level spells, 1/2 of clvl's worth of spell slots. Eg: 4th lvl regains 1 2d level slot or 2 1st lvl slots. \$\endgroup\$ – KorvinStarmast May 18 '16 at 20:13
  • \$\begingroup\$ 10th level spell slots are the new thing \$\endgroup\$ – Olorin May 18 '16 at 21:39
  • \$\begingroup\$ How did I miss that? Fixed, now. \$\endgroup\$ – J. A. Streich May 18 '16 at 21:39

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