Introduction

It seems the internet is littered with posts about players complaining that their Warlock just doesn't have enough spell slots, or that if they don't get that many short rests in a day they just become eldritch blasting machines. This invocation is designed to let Warlocks stretch their resources out a bit longer at risk of being less effective after a short rest. Is this Eldritch Invocation balanced?

Splinter Casting

Prerequisite: 3rd level

As a bonus action you may
splinter a spell slot into two. Choose a Warlock Spell slot. That slot
splinters into two slots with levels that sum to the level of the
spell slot that was splintered. You decide the split. When you
splinter a slot, any splinters from previous usages of this feature
that are related to the slot you are targeting are lost and cannot be
regained until you finish a long rest. On a short rest, all splintered
spell slots which were not lost recombine with splinters from their
original spell slot. On a long rest or by using the Eldritch Master
feature, you regain lost splintered spell slots, and all splintered
spell slots recombine with splinters from their original spell slot.

Thoughts

This invocation allows Warlocks to get more mileage out of their spell slots now at the cost of getting less mileage out of their spell slots later. While you can always splinter each of your slots once per short rest without any negative consequences, further splinter casting will reduce the benefits of a short rest by only letting you recover a weaker spell slot. If you want to be more like a traditional caster, you have to become less like a Warlock.

This invocation is ideal for Warlocks who want to cast more low level spells without feeling like they wasted a precious spell slot (Like hexblades with shield for instance), or for Warlocks who play in campaigns where they don’t get the opportunity to short rest very often and need to be able to stretch their resources. This invocation is of no benefit to the warlock who just wants to use their biggest spells as often as they can.

Isn’t this just a copy of the Sorcerer's Flexible Casting?

Not quite. Flexible casting is capable of creating all new spell slots using sorcery points, while splinter casting is all about splitting existing spell slots into smaller more usable chunks. Though I guess flexible casting also allows that, as a sorcerer can convert a spell slot into spell points, and then use those spell points to make more slots of lower level. The downside of the sorcerer doing this is that the conversion rate from spell slots to sorcery points back to spell slots is a net loss.

While at first glance it seems that splinter casting is strictly better in this regard, repeated splinter casting without first using some of your splintered spell slots can lead to you completely losing spell slots until your next long rest. Also, repeated splinter casting will lead to recovering less potent spell slots after a short rest.

Balance

While I concede that I am biased in this matter, I think this invocation is fairly balanced. In my opinion, the costs of an invocation slot and the penalty for repeated splinter casting makes up for the added flexibility. Also even if you splinter cast as much as possible you still have less spell slots of lesser level than the other full casters.

Another reason I created this invocation was to try and dissuade Warlocks from multi-classing into other classes just to get more spell slots. I also deliberately worded this invocation to make it so that it only works with warlock spell slots. This means that other classes which multi-class into warlock will gain minimal benefit from taking this invocation without investing a lot of Warlock levels. I suppose sorcerers can benefit from multi-classing and taking this invocation as it can make their flexible casting a bit more flexible if they only want to turn part of a warlock slot into sorcery points. I am not aware of any synergies that would create a serious power imbalance when combined with this invocation, so I think it can be judged on its own merits alone. Also, as I mentioned earlier, this invocation is only good for casting more spells of lower level. A warlock who wants to always be casting their biggest spells as much as possible gains no benefit from this invocation.

As for action economy, I modeled this after flexible casting by making splinter cast require a bonus action. The requirement of a bonus action in battle, and the limitation of needing to cast before splintering again to avoid losing a slot should make abusing the the added flexibility harder while still making it usable.

I picked level 3 as the minimum level for this invocation mostly because that is the first point in which you could actually use it. I'm open to the consideration of making this invocation require a higher level, but I currently feel that the level/number of spell slots themselves are sufficient to limit the power of this invocation as you level up.

Conclusion

I'm really interested in getting feedback on this Invocation. I feel like it has really great flavor and seems to fit the warlock theme well even though the invocation aims to shore up a common warlock weakness. With that said, It is entirely possible that I am missing something that makes this invocation just way too powerful.

Examples

In response to the comments asking for examples of usage:

Lets start with a 5th level warlock, which has 2 spell slots that are level 3. Say I want to cast Hex at first level, so I split one of those slots into 1 level 1 slot and 1 level 2 slot. I now have a 1 level 1 slot, 1 level 2 slot, and my other level 3 slot. If I finish a short rest now, the level 1 slot and level 2 slot will combine leaving me with my original 2 level 3 slots.

However, its when I want to splinter a slot multiple times that things get more interesting. Lets take that same level 5 warlock example, but this time I want to cast as many level 1 hexes as possible. So I splinter one of my slots into a level 1 slot and a level 2 slot. Now if I try to splinter the level 2 slot, the level 1 slot will vanish (I hope I used that slot first!) leaving me with just 2 level 1 slots. after a short rest, only those 2 level one slots combine, leaving me with 1 level 2 slot and 1 level 3 slot. I am now stuck with smaller slots until I finish a long rest which allows me to regain those slots.

So lets do one more example with a level 20 warlock. As a level 20 warlock I would have 4 level 5 slots. Lets say I want to cast as many level 1 spells as possible. By repeatedly splintering I should be able to cast a level 1 spell 20 times, but I have to take a couple limitations into account: I need to cast a level 1 spell after splintering a slot, but before splintering it again, or that spell slot will be lost before I can use it, and each time I splinter a slot again, I will only be able to recover a smaller slot overall after a short rest. In this case, after I splinter my slots repeatedly to get all 20 level 1 castings, I will have lost 12 slots of level 1 spells and be left with just 8 level 1 slots. After a short rest, those 8 slots will recombine and leave me with just 4 level 2 slots. I will not be able to get back to my original 4 level 5 slots until I finish a long rest.