Just to toss out more ideas.
Limit in combat actions by player actions.
I.e. player uses their bonus action to move a skeleton, action to make it attack, reaction to make an opportunity attacks.
Scaling to commanding 4 at once.
Commanding them takes concentration, but they will just stand...
IMO, id your doing a full class, make it a generic Summoner class. You're going to need nearly all the same mechanics if your summoning undead horde or elemental swarm.
IMO, the spell is stronger if you have bodies.
You don't want a campaign on a deserted island to completely remove all the features.
Side question. Why human skeletons? Seems like animating undead ants would be easier.
Just to bullet point things I would want in an undead swarm
Grapple
Difficult terrain
Moves slowly, not slowed by Grapple
Low but unavoidable damage
Size is based on HP/damage/spell slot
Grows/heals over time, possibly as an action.
Bonus HP/size if you include a corpse
Experimental thinking...
Seems perfectly reasonable for a DM to allow Summon Undead Horde to push a rock. Same as any other summon.
Which is probably a good reason to use a stat block instead of a zone that I initially suggested.
You got 1 skeleton by level 1 (which is less than 3rd). And your army grows every 2/3 levels after that.
That was the post I quoted.
Didn't see a way to get 10, but there's a few levels left.
Which is great if you don't have too many battles in a day.
Sorcerer's are best against a few powerful enemies. Not so good against 6 battles a day containing 5 easy enemies each.
Warlock 1 can get you a skeleton familiar.
Beastmaster 5, companion and summon beast spell.
Battlesmith 3, construct
Paladin 5, find steed
Wizard 5, unseen servant, phantom steed.
= that's 7 at once.
Maybe Fathomless 3 to get a tentacle, not sure id you would count that or not.
1 spell for utility. Warlocks can already get a skeletons as a familiar.
Also I don't see any reason why the swarm can't shoot. Maybe as a higher level thing, a Necromancer subclass thing, or such.
i'm not sure that's true.
They want an "army" to attack with, sure. And maybe a permanent undead servants. But unless i missed it, I still haven't seen anyone here say they want to roll for individual creatures.
We had other spells already make similar changes and it passed first try...
IMO, that's more of a Warlock than a Necromancer.
I realized the spell schools for those spells are "neceomancy", but i never got why they where categorized in the first place.