Chief defense against Mind Flayers at high levels.

Would this protect a fiend from a paladin's divine sense? 

I don’t think so, but I would say it’s up to the DM’s discretion.

I wonder if this spell or any other could be used as a sort of sealant against spells or effects like True Seeing / True Sight ?  I always found it a bit frustrating that there was no way for players or Monsters to be fooled as soon as they got that ability.

Yep, the spell seems to cover any and all divination spells and effects.  When it mentions it protects from even Wish I think you're covered.

If someone near you is targeted by a divination spell or you're near a Clairvoyance or Arcane Eye would this stop you from being seen or heard? I've ruled yes but I'm wondering what others think.

This is almost an up cast of non detection so ya it should

The Nondetection spell can also fool True Seeing, although it cannot best innate Truesight.

It's a shame it has to be a willing target. Hit an Elder Brain with this and cut it off from all its telepathic contact. 

So, I just opened up this option as a 15th level Bard.  I'm liking the idea of casting this at the start of every day to offset my terrible WIS save and the fact we go up against a lot of charmers and charm effects.  Does this seem like a worthwhile idea?

Quote from Wraethrax >>

So, I just opened up this option as a 15th level Bard.  I'm liking the idea of casting this at the start of every day to offset my terrible WIS save and the fact we go up against a lot of charmers and charm effects.  Does this seem like a worthwhile idea?

 

 

 

Beyond 20

 

 

 

 

 

 sure just nab magical secrets cast this take a long rest and you got perma imunity

How does this spell work with Awakened Mind or Voice of the Chain Master? Does it just cancel the telepathy of those abilities?

I just realized...this might protect you from the Eye & Hand of Vecna

I don’t think Mind Blank cancels telepathy. It stops effects that could read thoughts, but telepathy isn’t that; it’s more like projecting words into someone’s mind instead of speaking the words to them.

Here are all the spells from all official books that Mind Blank protects from as of today (let me know if you see mistakes).

I've named only the strongest reason why Mind Blank protects from each spell. There are 5 cases: 

1. Mind Blank makes you immune to Divination spells. You are unaffected by them - They fail to gleam information from you (e.g. the True Seeing spell doesn't reveal your invisibility) but also you can't gain their benefits (e.g. you can't cast True Seeing on yourself). 
2. The spell tries to set the Charmed condition and fails entirely.
3. The spell doesn't try to set the Charmed condition, but anyone who can't be charmed is still immune to this spell.
4. The spell tries to affect the mind and fails.
5. The spell deals 0 psychic damage, but other effects of this spell might still apply.

I've left out from the list cases with prerequisites. For example if a creature is first affected by a negative condition affecting their mind, then Mind Blank is cast on them and then a restorative spell is cast to remove the negative condition. Mind Blank then blocks the restorative spell, because restoring the negative condition would affect the mind.

Would this spell protect against a magical weapon's effects?

Like a sword that can warn its weilder against threats/hostile intent?

Quote from Kelain >>

Would this spell protect against a magical weapon's effects?

 

Like a sword that can warn its weilder against threats/hostile intent?

 up to dm, but i'd say yeah, the sword can't read their mind because of the spell

Awesome post vigo!

The description states that spells and effects to a similar power to a wish spell fail at gathering information on the target. Would that include a cleric's Divine Intervention?

no as a divine sense is not a mental observation