What are the mechanics of an Arcane Trickster using an Owl familiar's Flyby ability to gain Sneak Attack?

Question

I'm coming from a 5e campaign where there were house rules for a lot of things, including familiars, and I'm trying to understand exactly how an Arcane Trickster would use an Owl familiar's Flyby ability for Sneak Attack. I know that if the familiar is within 5 feet of an enemy I as a rogue can use Sneak Attack if I hit that enemy, and I know that the flyby ability means an owl familiar doesn't provoke opportunity attacks.

What I can't figure out is exactly how all the pieces fit together given that the familiar acts on its own initiative. Like, if the familiar has a lower initiative roll than I do, does the familiar hold its action until my turn, and then do a flyby of my opponent, and then I attack? Or does the familiar do a flyby when its turn comes and then I just keep that in mind when I attack? Or am I misunderstanding flyby and it's actually movement rather than action?

Let's say I'm in solo combat with two enemies and the initiative order is Enemy 1—>Owl familiar—>Enemy 2—Me.

Can I both get sneak attack by having the owl within 5 feet of my target and have the owl avoid attacks of opportunity? If so, how and when do I do it?

Answer 1

Owl uses the Help action, rogue uses the Attack action

The owl familiar can approach to within 5 feet of the enemy, use the Help action, then fly away. As was discussed in this previous question, a character doesn't need to stay next to the enemy after using the Help action for their ally to get advantage on an attack. An owl's Flyby ability means it won't be vulnerable to opportunity attacks while doing the last step of flying away (which is why you might prefer that form of familiar over something else). For a rogue, attacking with advantage also enables Sneak Attack (assuming there's no reason they'd also have disadvantage), even if there's no other ally nearby.

Held actions are only needed in defense against the combo

The combo is not foolproof though. Clever enemies will see what is happening and adapt. For instance, if they have ranged weapons, they might prioritize bringing down the owl by sending an attack or two its way, even if they have disadvantage on their attacks from the rogue being up in their face. And melee-exclusive monsters can hold their action to attack the familiar when it swoops down to be near them. Familiars have very few HP and low armor classes, so a single attack is often enough to do them in.

The combo is good, but probably not overpowered

Spending an hour resummoning the familiar after a fight is often impractical in the middle of a dungeon (even if you have the material components available), so the rogue can't exclusively rely upon using their familiar for their sneak attacks, even if it is very good when it works. A crafty DM might want to get rid of the rogue's familiar in an earlier fight (even at the cost of doing less damage to the rogue) if they don't want the combo to make the fight against the final boss of the dungeon too easy!

Different monsters' reactions can help with world building

A particularly skilled DM might use different reactions by different kinds of monsters to clever combos like this one to teach the players about the monsters, and about how they fit into the wider game world. If you try this trick on an ogre, it may keep on working indefinitely because ogres are pretty stupid and often get tricked into things by other creatures (such as the BBEG). If you try it against a gang of scheming goblins, one might catch on quickly and call out a warning to the rest (do any of the PCs speak goblin?), because goblins are reasonably intelligent and work well in groups. If you try it against a wizened ancient dragon, they may see your tricks coming a mile away and react appropriately even before you've used it against them even a single time (as a long-lived creature with truesight, that dragon has seen much more powerful tricky maneuvers fail many times before, and it's not at all hard to obliterate a familiar with a big AOE breath weapon that also gets most of the rest of the party).

Answer 2

Use your action to Ready an attack for the Owl's flyby, and have the owl use Help.

This method allows you to do exactly what you're trying to do. On your turn, you use the Ready action to make your attack, with trigger "my owl is within five feet of my target". Then on your owl's turn, the owl flies to the target, triggering your readied attack with Sneak Attack, then flies away.

This tactic can be made even better by having the owl use the Help action when it reaches the target, giving you advantage on your attack.

You're a rogue. You won't feel like you're missing out on Extra Attack when you use Ready, because unlike fighters, your secret sauce works even when it isn't your turn.

If your Owl is immediately before you in the order, you can make the attack on your turn.

This method only works if your target does not take its turn between your owl's turn and your own.

• Owl flies to within five feet of target.
• Owl uses Ready action to fly away from the target after you attack.
• Your turn, you attack with Sneak Attack.
• Owl uses reaction to fly away.

If the target has a turn between the Owl's turn and your own, the owl is vulnerable to melee attacks from the target while waiting for your turn.

Talk to your DM about commands and narrative.

There is one final consideration here, and I have played this both ways. You need to discuss with the DM about how to handle the commands given the familiar. For example, at one table, the DM let me just control the familiar as I would my own character. However, at another table, the DM required that anything the familiar did on its turn had to be the result of a telepathic command issued in-character on my own turn. If your DM requires in-character commands, these situations might get a little weird or difficult to reproduce.