I have a druid in my party who is about to hit 7th level, and thus get her first 4th-level spell slot. Because she's been having a lot of fun with the 3rd-level spell Conjure Animals, I've been preparing for her to love the 4th-level spell Conjure Woodland Beings. 

Now, Conjuring Woodland Beings allows you to summon up to 8 fey creatures of CR 1/4 or fewer. One of those creatures is a pixie.

Pixies can cast, once per day each, Confusion, Dancing Lights, Detect Evil and Good, Detect Thoughts, Dispel Magic, Entangle, Fly, Phantasmal Force, Polymorph, and Sleep.

So, if she summons eight of them, she'll be able to command them to cast all those spells. This is basically giving her, with one 4th-level spell slot, access to 8 polymorph spells, 8 sleep spells, 8 confusion spells, etc.

Please tell me I'm missing something, because that seems disgustingly powerful to me.

Talking about rule as intended, the DM decides which creatures are summoned. The players decides the quantity and the CR.

But, even if the players summons 8 pixies, keep in mind that pixies have 1 hit point and most of those spell available for a pixie require concentration.

Also, if the druid gets hit and fails the concentration save, he/she loses the pixies and pixies' spells.

You are right, however... a burning hands, magic missile or AoE will often destroy the pixie horde issue.

Player love to spam that combo, btw.  Just be prepared as the DM to counter such - 1/4HD creatures with mythic powers are only amazing if they get to take their action  - most of the time, they are a worthy lightning rod for soaking up spells or attacks.

AND if it gets out of hand, one creature that can cast the 4th level spell against the players will promptly address spam attempts of the use of such.

OMG that changes everything. I had no idea the DM chooses the creatures that are summoned; I thought the caster did. The spell text is not explicit.

THIS SOLVES MY EIGHT GIANT POISONOUS SNAKES PROBLEM TOO

Those things were a serious pain in the butt.

Thank you!

I would caution to DM around.  Find fights where pictures and poisonous snakes won't help much...  But don't leave them feeling the DM always screws them with 8 bunnies....

I have a party with two very strong characters: one with passive perception over 25, the other a Mystic.  Plus a walking fireball generator.  Design encounters that will let them have fun, but their strength does not overpower the group. Example, high perception meant the character was first to see Gauth and be stunned.  

Well balanced encounters will let players play the characters they want without dominating.

If that does not always work, let someone summon pixies and snakes on them 😎😂

I ran into this in a campaign recently as well. Something to remember - fey creatures can be rather.. fickle, and can do as they please when they're not being commanded. It wasn't uncommon for the caster to wind up with their boot laces tied together. I came up with a 'prank chart' for when the player would cast it. 1-10 got nothing, 11-20 got a trick at the end of their casting. Nothing awful, boot laces tied together, hair braided in an odd way, someone turned into a sheep at a non-critical time, etc. I don't try to punish the player, I just want them to know that they're conjuring beings that aren't entirely under their control all of the time and have a mind of their own.  Let's not get started on a prank chart for a Satyr!