What is wrong with me?! The sentence "This spell has no effect on undead" is making me laugh.

This is the spell one would use on Giants, right?

Yes indeed - this is the one you would use on Giants.  Will also work on Humanoids too though.

Does Mind Blank block this spell? Is this spell considered a 'charm'?

Quote from Iron_Theurge >>

Does Mind Blank block this spell? Is this spell considered a 'charm'?

 This is an enchantment spell, like most that cause charm. However, it causes the paralyzed condition, not charmed, so mind blank won't protect you from this.

Spells that can are ones that block spellcasting or break the direct path to the target, such as tiny hut, resilient sphere and even wall of force if placed correctly.

This spell doesn't affect undead. Is there a spell similar to this that will hold/immobilize undead where they stand? I know some class abilities given to paladins and clerics do something along those lines, but I'm curious regarding spells. 

This is why you should always have Legendary Resistances on your bosses. Let my first BBEG be the last victim.

It's also available for Monster Slayer Ranger

With this being a 5th level spell, are there any advantages that this spell has over Banishment; a 4th level spell? It seems like Banishment is more effective. It’s a Charisma saving throw and they creature doesn’t get to make a save to return every round. Am I missing something here about Hold Monster?

Paralyzed makes attacks made within 5 feet automatic crits, which makes this a very good spell to DPS down a powerful monster. Banishment removes a target from the field, but doesn't help you kill it beyond letting you kill its allies first.

Would this work on a dragonborn?

I know this is a long time to wait for a reply... but....

Banishment has the potential to be a permanent solution, but there's a few caveats.  1) They aren't natively from your plane.  2) They don't return to your plane (which, since they were there in the first place, one assumes they might crossover again).   3) You don't stumble upon them when you're in THEIR home plane.

Hold Monster is not, in itself, a permanent solution to an enemy problem.  However, it does let you keep an eye on them the whole time, and they can still be attacked (with increased efficacy) while they are being held.  For most creatures, dead is a better solution than banished.

Beyond that, there's circumstantial reasons for each.  Making a creature *gone* is good for some things.  Making a creature still and quiet, but still able to see and hear is good for other things.  Think creatively, and I'm sure you'll find a lot of use cases for each.

Isn’t it also available for Monster Slayer Rangers?

They are considered "creatures", so yes

a knight rushes towards you, lance lowered, horde at full speed.  hold creature on the horse.....

hunchback of based god

Not a charm but would be able to use Mind Blank to prevent it. The wording of mind blank is 

"The spell even foils wish spells and spells or effects of similar power used to affect the target’s mind or to gain information about the target."

Due to the fact that Hold Monster is a Wisdom based save, that would suggest that the way that it works is an influence on the mind and therefore blocked by the mind blank. However, you would no give creatures that have advantage against charm effects the advantage, if that makes sense. 

Use this to help your Intellect Devourer buddies get into heads.  Paralyzed includes Incapacitated so... straight to Int contested rolls.  

Quote from bschloef >>

Not a charm but would be able to use Mind Blank to prevent it. The wording of mind blank is 

"The spell even foils wish spells and spells or effects of similar power used to affect the target’s mind or to gain information about the target."

Due to the fact that Hold Monster is a Wisdom based save, that would suggest that the way that it works is an influence on the mind and therefore blocked by the mind blank. However, you would no give creatures that have advantage against charm effects the advantage, if that makes sense. 

Going by RAW, no it would not be able to. Mind Blank says nothing about it.

Wisdom, Intelligence and Charisma are often used as abilities for saving throws against general magical effects anyways, not just ones that affect the mind. So this spell being a Wisdom save suggests nothing of the sort. In fact if you ask me, neither this spell nor hold person even touch the mind, instead making use of magical force to hold the body in place. Thus the creature isn't really paralyzed at all, just so thoroughly restrained they might as well be.

Quote from CoolerKoolaid >>

Quote from bschloef >>

Not a charm but would be able to use Mind Blank to prevent it. The wording of mind blank is 

"The spell even foils wish spells and spells or effects of similar power used to affect the target’s mind or to gain information about the target."

Due to the fact that Hold Monster is a Wisdom based save, that would suggest that the way that it works is an influence on the mind and therefore blocked by the mind blank. However, you would no give creatures that have advantage against charm effects the advantage, if that makes sense. 

Going by RAW, no it would not be able to. Mind Blank says nothing about it.

Wisdom, Intelligence and Charisma are often used as abilities for saving throws against general magical effects anyways, not just ones that affect the mind. So this spell being a Wisdom save suggests nothing of the sort. In fact if you ask me, neither this spell nor hold person even touch the mind, instead making use of magical force to hold the body in place. Thus the creature isn't really paralyzed at all, just so thoroughly restrained they might as well be.

 If it were magical force, it would be transmutation or abjuration, maybe even evocation if you're completely mad (they made wall of force evocation, after all.) There also wouldn't be target-based requirements (e.g. hold monster can't affect undead, hold person only affects humanoids). It's your table, but I'd say it counts as something mind-affecting, and thus would be blocked by "The spell even foils wish spells and spells or effects of similar power used to affect the target’s mind." Technically, it only works on thing of similar power to wish, but that's as dumb as a counterspell or globe of invulnerability that only works on spells of exactly 9th level.