The artificer class has the Infuse Item class feature, which allows it to make "effectively a prototype" of a permanent Bag of Holding using the Replicate Magic Item Artificer Infusion, which, as far as I can tell, is an exact replica of a real Bag of Holding, only temporary. It has all rules text of a Bag of Holding, including the following:
Placing a bag of holding inside an extradimensional space created by a handy haversack, portable hole, or similar item instantly destroys both items and opens a gate to the Astral Plane. The gate originates where the one item was placed inside the other. Any creature within 10 feet of the gate is sucked through it to a random location on the Astral Plane. The gate then closes. The gate is one-way only and can't be reopened.
It was already ruled in the text of those items that Bag of Holding is a "similar item", meaning placing a Bag of Holding inside a Bag of Holding instantly buys all creatures within 10 feet of it a one way ticket to the Astral Plane.
So then, is there anything at all to stop a party from having two party members, both artificers (since a single one cannot make two bags of holding) from creating a "Bag of Holding Bomb" by strapping the bags together, lobbing them at the enemy, and then placing one bag in the other with a spell like Telekinesis?
If the Telekinesis spell is readied as a reaction to the bag being within 10 feet of an enemy, there would then be no saving throw or other way for them to avoid the warp, not even a legendary action.
I am aware of tricks a DM could use to avoid this, maybe the creature is smart enough to recognize the danger and ready reaction of it's own to steal the bags, maybe someone in the Astral Plane gets annoyed at all the new visitors and starts sending them back, with some extra planar creatures tagging along as a bonus, etc.
But DM tricks aside, is the "Bag of Holding Bomb" viable under RAW? In RAW, is it unavoidable, or is ruling that the creature can make a DEX save since it is being used as an attack still RAW? (I assume not, unless I missed something)
Best Answer
It's viable under RAW ...
... as discussed in this Q&A. Beyond that, any ruling on how to avoid the attack falls into a host of situationally dependent details. It's difficult to arrive at a general answer that fits all situations.
Turn order can influence the success of this tactic
One significant issue will be the initiative score of the two artificers. If their initiative scores are not identical, or not sequential, there is a turn-based "delay" in a given round as the telekenesis step is awaited in the turn order after the toss step. If the creature they want to send on holiday to the Astral plane has a reaction, movement, or an action before that telekenisis step, they can probably "see and avoid."
Whether or not they realize the nature of the threat you can emulate as an Intelligence Ability check, if necessary as a DM.
Your use of the Readied action accounts for most of the above problems.
Legendary Actions might interrupt this
Creatures with legendary actions pose a case where, depending on what the legendary action is (functionally, a legendary action works like a reaction taken on another creature's turn).
If your party surprises the creature, I think you've got 'em! 😉👍
But if you haven't surprised them, you run into a turn based mechanics problem of "when is my readied action going off versus when did the bags land there versus when did that reaction occur?" This needs a DM ruling.
If the telekenesis reaction isn't before the other artificer's turn is over, who is to say when it happened in terms of 'when did the bags land near their target?'
If the telekenesor interrupts his ally with his reaction, the toss never goes off, or does it? DM ruling needed. Even then, if I have a an adult dragon with a Wing Attack, that has this effect as a legendary action ...
It can move out of the way, and the wind of that force can arguably move the bags. Likewise, but to a lesser extend, with the tail attack. If the dragon chooses to attack the pair of bags rather than the pair of artificers.
While it doesn't say explicitly that it knocks small loose objects any distance, one can easily rule that it does and it makes sense from the PoV of verismilitude.
More generally, any legendary action that includes movement or an ability to move the pair of bags could potetially frustrate such an attempt. The DM has to rule "whose reaction goes first?" in a case like this - the other artificer, or the targeted creature? I'd be inclined to use either Dexterity or Wisdom Contest (Basic Rules, Chapter 7, p. 61) to adjudicate that as a DM.
The creature's allies may likewise have an action available, or a reaction, that interrupts the two artificers getting their "lobbed pair" + "telekenesis" sequence to occur before any interruption of the sequence. But to thoroughly frustrate your tactic, they'd have to be readying an action to "throw back whaterver is thrown at our boss" or have an ability similar to the Monk's Deflect Missiles (uses a reaction). Otherwise, your use of readied action should prevail.
Again, a Dexterity Contest is probably the best way to resolve "whose reaction comes first?" if one is used as a counter to this tactic.
If the target has a familir, like an imp, the familiar may be able to do a cinematic "toss the grenade back!," if it is able to use a reaction or has an action readied. You (as a DM) could call it a "help" action or an "interaction with an object" in terms of how that fits into what familiars can do. I'd still call for a contest as DM.
Is a Dexterity save against this RAW?
No, since it's not a spell attack. The bags are thrown like a flask of oil or alchemist's fire, it seems, or holy water, but the target to hit is "anywhere within 10' of the target creature." That's not a very high armor class. I'd estimate an Armor Class of 10 to start with, and the bags are an improvised weapon. That leaves a chance of failure in terms of "We threw it, but missed by throwing too far or not far enough!" But it's not beyond reason to rule the Armor Class as lower than 10. This leave us with this DM ruling again: What is a reasonable armor class for a CEP of 10'? (CEP = Circular Error Probabaility, a measure or accuracy/precision on bombs dropped or mortar rounds lobbed ....)
As an aside:
I love it when people come up with clever little tactics like this. :) FWIW, and one artificer can make two bags to try and do this ....