Can a Rogue exploit a tiny familiar for automatic Sneak Attack in melee?

Question

A Rogue's Sneak Attack can be triggered "if another enemy of the target is within 5 feet of it". This other enemy may be a familiar. Being tiny, a spider familiar can mount the Rogue without limiting their actions, thus enabling them to use their Sneak Attack in melee while it sits e.g. on their shoulder.

One can refine this strategy to increase the spider's safety: Using the Cunning Action to Disengage, the Rogue can get in, attack, and get out back to a relatively safe space, never leaving the familiar in danger. The familiar might also take the Dodge Action, just in case.

Am I missing something? What's the catch? How can the DM counter such a strategy?

Answer 1

It's possible, but there is a couple of DM approvals required to kick this off

Let's start at the beginning, you've got a familiar that wants to be 'on' your character as a means of providing 'safer' Help action economy.

Mounting a player character (DM approval)

Generally, two characters can not end their turn in the same space. The question of mounting another creature then comes into play. This is the first step in a DM determining whether or not something is feasible. While RAW it's possible, a DM still needs to determine if a spider can actually mount a humanoid. It's not unreasonable to say that a spider does not mount a humanoid and that the proposed combo isn't viable.

But let's say they do.

Squishy Familiars and Action timing

First off, find familiar doesn't RAW allow the caster of the spell to control the familiar on their turn. In fact, the familiar needs it's own initiative (PHB, 240):

Your familiar acts independently of you, but it always obeys your commands. In combat, it rolls its own initiative and acts on its own turn.

Again, the DM will need to houserule to allow the timing of this to always work. Of course, if giving it's own initiative and they're after the Rogue, they can always hold their action to Help as the Rogue closes in.

But let's say this all works out in terms of initiative order. At this point, you still have a very squishy little spider. It's easily killed via AOE attacks or most direct attacks due to it's low AC and HP.

There's still the option of not using Help for advantage and Sneak Attack, but just being within 5' as you've noted. Then the timing is less important except for it being on you at the start of combat.

And there remains a cost to bring it back the next combat. If the caster isn't a ritual caster (like the proposed Arcane Trickster), they're going to need to burn a spell slot and the required materials. It's not a bad trade-off for the increased damage output with Sneak Attack, but it is a cost that's higher than a caster with Ritual Casting.

Being an enemy (DM Approval)

If not using the Help action, then all the creature is is a spider. It's not involved in the combat or the encounter in anyway other than simply being present. If it's not actively doing something, it's a bit of a stretch that someone would consider it an enemy.

What's good for the goose...

Finally, we've got a player using a semi-reasonable tactic. The tactic is more commonly used with the owl's flyby and trusting that a creature won't target it after, but this is very similar to that. It's a big part of having a familiar and isn't necessarily bad.

But if it's always working, I'd fully expect the DM to set up monsters who also use this. The biggest thing that I as a DM always try and work with is allowing players freedom to come up with cool stuff, but if it's borderline and used too often, then i'll have a talk with them.

Owl Fly-By and my experience

When I had my wizard (before he died :( ) I used the fly-by owl to grant Help. I did it more often for my friends then for myself, but I wasn't the class that would gain a real benefit like a rogue (I did generally give the Help to the Rogue.) The DM was skeptical, but understood the mechanic. And at times they directly targeted the owl, but at other times did not. It was really based on the monsters, their intelligence, and the threat levels. But a monster realizing that this thing is making another creature really hurt them, they're gonna get rid of that thing.

Answer 2

The pet spider is not an "enemy of the target"

How can a DM deal with that apart from flat out prohibiting it?

It's easy to rationalize, why this wouldn't work. The Sneak Attack requires "another enemy of the target" to be within 5 feet of it. "Enemy" is not a game term, its definition is up to the DM. A pet spider, that are not directly involved in the fight, but instead is just sitting in someone's pocket (or shoulder, whatever), clearly is not "an enemy" of anyone.

Also, there is no ignorable "fluff" text in 5e rules. The Sneak Attack description states:

you know how to strike subtly and exploit a foe’s distraction

Since there is no distraction, there is nothing to exploit.

Why allowing this would be bad

The DM's responsibility is to facilitate fun for everybody, and no-brainers are not fun. This exploit, as it was described — have a spider mount only for activating a mechanical feature — is a no-brainer. It creates an unsatisfactory precedent, contributes nothing to the story, and looks stupid. Luckily, the player's idea can be easily salvaged.

Ask "how do you do that?" That allows the player to contribute to the story. Maybe the spider jumped out and frightened the foe. Maybe the spider just sits still on the rogue's shoulder, and the foe feels unease because of their arachnophobia. When an exploit is allowed situationally and is justified, it gives the player mechanical advantage, while still feeling "fair" for others.

Answer 3

Apparently we have switched to mounting rules and I must edit my response:

RAW yes but a DM would probably tell you No

If the Spider is inside the Rogue's pocket (this is the most relatively safe spot I can assume, that or inside the backpack of the rogue, since it is now out of sight and has total cover), even if it is technically "mounting" the rogue and within 5ft of the enemy, because it doesn't actually have a direct line of attack to the targets (as it cannot attack through the pocket) it is hard to argue that it is providing any type of meaningful distraction to the enemy.

Were the spider perched on the Rogue's shoulder this would be different, it can threaten attacks from this vantage point and therefore can provide a meaningful distraction, it is, however, not a relatively "safe" spot to be as it can easily be attacked from this point.

Answer 4

Am I missing something?

Not specifically. This is technically legal, just like the standard owl shenanigans with Find Familiar are.

What's the catch?

Familiars are fragile, and can't be expected to last long in combat. A single attack targeting them is enough to take them down.

How can the DM counter such a strategy?

AoE damage. A spider has 1 hit point and will die to any AoE spell that it's targeted by with no failure chance.
1 dart from magic missile will also kill it with no failure chance.
Even better would be readying one of these to go off as the Rogue approaches, to force them to change targets or lose Sneak Attack damage that round.

If you don't think these methods are good enough, an enterprising DM should simply have several enemies use this tactic, and then watch how the players deal with it.

If you don't think those methods are good enough, you should use the most powerful tool in a DM's arsenal:
Talking to the player who's doing it. Find out if they think Rogues are underpowered, or if they just like Minmaxing, or if they think that unintended ("clever") tactics are supposed to be stronger than standard tactics.

Answer 5

The DM can use a readied action

Disengage only prevents opportunity attacks. A DM can instead have a hostile creature ready an attack and wait for the rogue or familiar to move into melee range to make the attack.

In this case, only dodge is of benefit, though that can be cancelled out as well if the creature had some way of gaining advantage on the attack.

And, of course, if a creature or one of its allies has the ability to cast spells, that opens up even more options.

Answer 6

Yes, this is allowed. No DM houserules necessary.

Your mechanics are correct, the spider can mount you, and it can trigger sneak attacks. One thing that other answers gloss over is that a "tiny" creature is not all that tiny. People are mentioning putting the spider in your pocket, but that is ridiculous. A tiny creature controls a space that is 2 1/2 feet by 2 1/2 feet:

Tiny 2 1/2 by 2 1/2 ft. Imp, sprite

This isn't a normal tiny spider, by real world terms it is as big as a cat. If you think about how nerve wracking it would be to fight a rogue with a cat sized spider sitting on their back, it makes the rules feel a lot fairer.

Your spider can mount you

The spider can mount you as an independent mount. You both retain your initiative orders and act independently:

An independent mount retains its place in the initiative order. Bearing a rider puts no restrictions on the actions the mount can take, and it moves and acts as it wishes. It might flee from combat, rush to attack and devour a badly injured foe, or otherwise act against your wishes.

There is no timing issues or problems to work out. The spider can mount the rogue at any time. Once mounted the spider can then take the dodge action for the rest of the encounter. There isn't any timing issues that need to be house ruled.

The spider is an enemy of your enemy

There are no specific rules for this, it's normal English. To say that familiars are not enemies is nonsense.

What's the downside? How can it be countered?

Everything you are doing is totally fine by RAW. There is nothing questionable or uncertain. So is this really overpowered? How can a DM fight back?

The spider has low AC, and hp HP. Even the weakest enemies will have about a 50% chance of hitting it, and will kill it in 1 or 2 attacks. If they decide they want that spider dead, it will happen quickly. Even if the familiar dodges, their odds of survival aren't great. Most AoE abilities will kill it instantly.

What's more, it is quite an investment for a Rogue to get a familiar. To use it in this way, only to have a goblin 1 hit the spider, would really suck. You need to be very careful.

In contrast, you could stand at 600ft range out of sight and undetected, hide, and attack with sneak attack AND advantage. It's easier and simpler and you get advantage!