Is this "Withhold Summon" feature problematic?

Question

I found this summoner class on DMsGuild, and it seems like a fun, balanced class that fills an interesting niche. One of the major features of this class is "Withhold Summon", an ability gained at 5th level that allows the Summoner to "shunt" a summoned creature into storage, prolonging the duration of the summoning effect. Note that this class is a 2/3rd caster which only has summoning spells. I'd like to know if this ability seems like it would be too powerful, as well as possible abuse cases. Particularly, I'd like to know if there are any multiclassing combinations I'd have to nerf or refuse to allow.

Withhold Summon

5th-level summoner feature

At 5th level, you gain the ability to shunt into a pocket dimension a summoned creature that is under your control and within 30 feet of you, as a bonus action.

While shunted away in that fashion, the target is incapacitated. It can breathe normally, doesn’t require sustenance, and can take a short or long rest, assuming it has sufficient time to do so. If the target was summoned through a spell, the spell’s duration is suspended until the creature is released.

As an action, you can release a shunted creature, making it reappear in an empty space within 30 feet of you. While there is no limit to the number of creatures you can shunt away with this feature, any concentration required must still be maintained. When you complete a long rest, for each of the creatures that are still shunted away, you must choose between expending anew the resource that was used to summon it or to lose the shunted creature. For example, if a creature was summoned using the summon monster spell by expending a 2nd-level spell slot, you must expend a 2nd-level spell slot at the end of the long rest to keep the creature shunted, or the spell is simply lost. The same applies for creatures summoned through other ways, such as with a class feature with a limited number of uses.

This is probably unrelated context, but the summon monster spell mentioned in the feature allows you to select a creature type, and the DM gives you a monster of that type with a CR up to 1/2 of the level the spell was cast at.

Note: I realized that my earlier question was probably too big for this site, so I decided to ask about this particular feature on its own.

Answer 1

Seems fine

The primary intent of this ability is to let you cast a one-minute summon spell at the start of the day, and then have it available when you need it. (So you don't have to say "oh, wait, wait, this looks like it might turn into a fight, everyone chill for sixty seconds while I summon my monster, I hope I'm not wasting a spell slot, okay now we can open that door...")

To me this seems like an obvious quality-of-life fix. I'm sure there will be people who argue that having to decide when to advance-summon your monster is a part of game balance, but from my perspective it's fine to let the summoner have a class feature to take care of it.

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A secondary feature of this ability is to extend the duration of a summon spell, so that a single summon can be useful in multiple fights.

But summon spells already last a full hour, so if you're doing some sort of dungeon adventure, a single summon is already good for several fights! (You just have to persuade your allies not to stop for a short rest until your summon is dead.) What are the odds that your DM's adventure includes multiple serious battles, with more than an hour span between any pair of them?

And, even if you do get in a situation where your DM has that many serious battles, how likely is it really that you can avoid getting targeted by an enemy and failing a concentration check and losing the spell anyway? How likely is it that your summon survives the whole fight?

This feature is very situational and unlikely to matter in practice.

Answer 2

Looks useful and mostly well designed

The immediate ways to abuse the feature one can think of is that one would shunt away a zoo of creatures, to then quickly recall them in a combat situation, but the restraints take good care of that. Most conjuration and summoning spells need you to maintain concentration and for those few that do not, you cannot accumulate summons over long rests for free.

This still could be a bit problematic if there was a homebrew spell that summoned some powerful monster with longer casting time and without concentration, but as both those features would be homebrew, one would need to look at them together, and maybe the solution there would be to fix the summoning spell instead.

The major benefit of this is that it can save you a few higher level spell slots: as most fights only last 3-4 rounds, and most conjuration spells last for up to an hour of concentration, this will extend the useful life of any concentration summoning spell for combat to the whole day. Just pop out your summons when you need it for a fight or some other service, then stash it away again to suspend the duration. While it is shunted for more than an hour, it also can short rest to take hit dice to heal, effectively doubling its hit dice and with that rounds of combat before it dies - that would not work if it ended after an hour of concentration. So in most cases, this can save you at least one higher level spell slot like conjure elemental, maybe more depending on how spread out your fights are, and how long you adventure in the day.

Most summoning spells take a minute to cast, making them useless for combat unless pre-cast. This gets around that, which makes all of them stronger, but as most of them have an hour duration, you in practice summon your monster, then enter the dungeon and have it along for the fight, and calling back the monster here still takes you a full action, so it does not allow you to double-dip and both “summon” a powerful monster and cast another full spell in the first round of combat.

One benefit that is not obvious is this part:

As an action, you can release a shunted creature, making it reappear in an empty space within 30 feet of you.

This seems to be lifted from find familiar and it does not say you need to see the space, it has the same issues: you now can "teleport" your minion to the other side of a wall or door, you can use it as a sonar for secret doors and passages by trying to call it back behind walls (which will only work if there is empty space there). And other than a familiar this can be a creature that is strong and smart enough to unbar gates.

If there is one thing I would fix about this, it would be to explicitly say that the creature cannot take anything along while being shunted, like find familiar says. Otherwise, there are many unclear rules interactions e.g. what happens to shunted objects when you drop concentration while shunted? You also then could use this to empty out closed treasure vaults, pop your minion in there, let them gobble up the treasure, shunt them again and pop them out next to you.

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P.S. Note that your linked "Summoner" class has a subclass called collector that does away with the concentration requirement for shunted creatures, and allows them to recall multiple creatures with a single action. That is a lot more problematic and unbalanced.