[RPG] Does Telekinesis stop restraining its target if the caster can no longer see the target

The rule requires that you not willingly end your turn in another creature's space. Sometimes you will be prevented from taking actions in order to make sure the rule holds true.

The DM always has jurisdiction over edge-cases like this and will often make rulings on consequences and benefits, so although I speak from the perspective of being a DM myself, my own interpretations will not always hold true.

Willing and unwilling do not have mechanical definitions, but here's how I would rule them for practical use.

Unwilling:

• Effects that have a risk but not a guarantee of forcing your turn to end in that space

Willing:

• Effects that guarantee you will end your turn in that space which are not hidden from player knowledge
• Effects coordinated with a party member to place you in a space.

Regarding your examples:

1. You must not willingly spend movement to end in the creature's space. In the case that they're forced unwillingly into the space after/before movement, such as by a grapple, RAW does not require action economy (misty step, breaking grapples, dashes, etc) to be spent on vacating the space.

   Sidenote to 1: The rules are unclear whether a player may receive their once-per-turn movement and not spend it to remain occupying the space, but this is clearly against the spirit of the rule. If a player has movement, I believe it should be spent to vacate the space. I also believe that actions a player controls (such as misty step and falling from above) should not cause the space to be occupied, but I would rule these on a case-by-case basis.

2. This is a tougher one to rule on. RAW you can attempt to spend movement to pass through the space and unwillingly have your movement reduced to 0 in that space. The creature must be friendly or your size class has to permit movement through it's space (size class overrules this general rule).

3. This would likely require a rollback. You willingly spent movement and then realized it was movement you couldn't use. You broke a rule, the DM will likely undo the action that broke it or offer you an alternative (such as taking disadvantage).

It would appear so

It's hard to know if it's intended or not, but it is a consistent way to interpret the rules, depending on how you interpret p.54 of the Monster Manual, which tells us that:

A demon can be forced to disclose its name if charmed

There are two ways of reading this into your question:

1. This specific rule overrides the general rules of Summon Greater Demon, and tells us that the only way to get a demon to disclose its true name is by charming it. The demon under your control via the casting of the spell is not technically charmed, so you'd need to charm it in order to learn its name
2. This rule describes one possible way of learning a Demon's name, but there are others. This makes sense because the paragraph in question also lists 'ancient scrolls' as a possible way of learning a Demon's name. It's consistent that threats, bargains or other means of control could also be used to illicit a demon's name from the demon itself.

I'm sympathetic to the second ruling; I don't see anything to suggest that the charmed condition is the only way to get a demon to tell you its name. Since the spell places no limit on what the controlled demon can be commanded to do (ie. commands are limited by what the demon can do), it follows that you can command the demon to tell you its name.

This seems counterintuitive and might be unintended - it would be unusual for the spell to specify that 'the demon has disadvantage on this saving throw if you say its true name' when the spell gives the means of learning its true name, albeit at the cost of an action at the start of the hour-long casting time.

I wouldn't allow it at my table, but from what I can see it's totally aligned with the RAW

Edit: I've been reading some other opinions on this, and I'm not 100% sure that it isn't intended.

It's also worth noting the absence of any rules which dissuade the caster from harming the demon, or causing it to cause harm to itself. Many creature-control spells allow the saving throw to be repeated or cause the spell to end if the caster or their allies harm the charmed creature, and explicitly forbid commands that will directly imperil the creature. This spell has no such caveats: You could literally summon a demon and command it to stab itself in the face with zero penalty. Considering that this is the extent of your control over the creature, it's consistent to infer that you could ask the demon to tell you its name.