In the same way that Dr. Who’s Daleks are an unstoppable race of space-murderers that can be thwarted by a flight of stairs, Arcane Eye would be a game-breaking spell if it wasn’t so bad at dealing with doors.

It allows you to create an invisible eye that floats in the air and can be directed wherever you want. It only moves at a rate of 30ft. per round, but once you cast it the spell lasts for an entire hour.

This gives it an effective range of well over three miles – more than enough to completely explore all but the biggest dungeons. The fact that it is invisible and (presumably) completely silent means that it doesn’t have the risk of being shot out of the air that makes scouting with magical familiars so dangerous.

The only thing that stops you from being able to cast this and ask the DM to save time by drawing out the entire dungeon map right now is its inability to pass through solid barriers, such as doors and windows. The rules specify that while it can go through small holes they need to be at least one inch in diameter – a stipulation that has prompted more than one group to break out the rulers and track down a door with an old-fashioned lock.

Unless you’re dealing with giants or a group that’s particularly keen on massive keys, this means that Arcane Eye is going to have a real problem with doors. In a dungeon or building where the inhabitants are moving around fairly regularly it’s possible for the eye to nip through while they’re open, but that still severely limits its effective range.

Does this mean that the spell is useless? Of course not!

For one thing, it makes scouting cave systems, mazes and other open areas absolutely trivial. It lets you spy through windows with impunity, read documents you aren’t meant to and generally be thoroughly sneaky.

The fact that it doesn’t blind your conventional senses means that it’s also a great way to avoid ambushes or watch for enemy reinforcements.

It’s a fourth-level spell so isn’t something you’re going to be throwing round without a thought, but in many circumstances it can provide excellent utility. If nothing else it can force the DM to think on her feet when you send your Arcane Eye out to map the villain’s lair without having to deal with the puzzles, ambushes and dead-ends designed to slow you down.

Rating: B

A solid utility spell that with its great potential balanced out by significant weaknesses. At first glance it looks a bit weak for a fourth-level slot, but remember that if it helps you to avoid a combat encounter it’s probably an excellent trade-off.

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Arcane Eye

School: Divination

Level: 4

Casting Time: 1 action

Range: 30 feet

Components: V, S, M (a bit of bat fur)

Duration: Concentration, up to 1 hour

You create an invisible, magical eye within range that hovers in the air for the duration.

You mentally receive visual information from the eye, which has normal vision and darkvision out to 30 feet. The eye can look in every direction.

As an action, you can move the eye up to 30 feet in any direction. There is no limit to how far away from you the eye can move, but it can’t enter another plane of existence. A solid barrier blocks the eye’s movement, but the eye can pass through an opening as small as 1 inch in diameter.