Phantasmal force/ Phantasmal killer

Quote from Agilemind >>

 If you create an illusion of a force cage around the target, then the target sees & believes their is a force cage around it. But If the target tries to touch the force cage their hand goes through it because it doesn't actually exist and their brain rationalizes some reason why they can reach their hand through a force cage.

 Is that what happens? Or do they play Mime in Invisible Box because they think they're contained? Or does trying to touch the cage count as taking the study action and if they succeed they realize it's not actually there, if they fail they're trapped?

Quote from Pantagruel666 >>

Quote from Agilemind >>

 If you create an illusion of a force cage around the target, then the target sees & believes their is a force cage around it. But If the target tries to touch the force cage their hand goes through it because it doesn't actually exist and their brain rationalizes some reason why they can reach their hand through a force cage.

 Is that what happens? Or do they play Mime in Invisible Box because they think they're contained? Or does trying to touch the cage count as taking the study action and if they succeed they realize it's not actually there, if they fail they're trapped?

 They are no more trapped than they could walk over a bridge if you made them believe there was a bridge across a chasm. The cage does not exist thus they are not trapped, if they make any attempt to escape they succeed in doing so, just as if they attempt to cross the bridge they fall through into the chasm. It is right there in the spell description.

Quote from Agilemind >>

 They are no more trapped than they could walk over a bridge if you made them believe there was a bridge across a chasm. 

The core difference there is: the affected character is not moving themselves through the bridge, they are being moved by an external force (gravity). Likewise, an illusory cage would not prevent some external force from grabbing the character and moving them -- phantasmal force only affects what the target can do of their own will.

I think it depends on how they try to escape and what the bindings are. if they are in a cage and shoulder rush it they end up out of the cage. if they try to smash it with their hammer it passes through harmlessly, and they rationalize why, they might mime in an invisible box because they know force cage can't be broken, though I'd consider either of those a study action.  if targeting the player I might roll for them or use passive. What the illusion is might shape the logical break free attempt is. Lets say your legs are manacled to the wall, do you just pull, do you smash it with a weapon who knows. But if you summoned a steel cage with dangerous looking spikes jutting out of it, is shoulder rush the option they would choose or would they try to break it with a weapon and keep some distance. You have now narrowed down the likely responses to something where they probably remain trapped. 

Quote from MyDudeicus >>

But if you summoned a steel cage with dangerous looking spikes jutting out of it, is shoulder rush the option they would choose or would they try to break it with a weapon and keep some distance. You have now narrowed down the likely responses to something where they probably remain trapped. 

 That completely depends on what the enemy is. A horse would panic at being confined and would fling hooves at a dangerous looking steel cage, or bolt out of it. An intelligent humanoid wouldn't. An wizard with access to Misty Step most likely would simply teleport out of it. But generally most creature that find themselves confined will make some attempt(s) at escaping and especially during a combat situation are unlikely to just sit back and chill until they are released. Phantasmal Force is not Domination, the affected enemy can willfully do whatever they normally would do when confined. They can move as they will, they can attack as they will, they can speak as they will regardless of what the phantasm is. Since only the affected target can see the phantasm it the target has intelligent allies with them, most likely their first response will be to shout out "Help me! I'm trapped!" to which the intelligent allies will respond "No you aren't, there's nothing there, come help us kill these guys!" at which point most creatures are likely to attempt moving through the phantasm. 

If you want to restrain an enemy, use Entangle, or Hold Person, or Earthen Hand, or Web, or any of the other spells that actually conjure physical restraints. 

There are not specific rules for what Phantasmal Force can and cannot do, because that would completely destroy the creativity that makes the spell fun for both the DM and the players. Consider the following possible use cases:

1. Distract a guard dog by having it see a big pile of delicious meat at the far away from where the party is.
2. Lure a bandit away from their camp by having them see a lost chest full of gold coins.
3. Trick an enemy to stepping off a cliff with a phantasmal a bridge.
4. Scare off one or more harpies by creating the phantasm of the shadow of an Awk flying overhead.
5. Confuse/Distract a T-Rex by phantasming an attacking Triceratops right next to it.
6. Trick an enemy into falling off a tower by phantasming the ladder to the wrong location.

Quote from Agilemind >>

Quote from MyDudeicus >>

But if you summoned a steel cage with dangerous looking spikes jutting out of it, is shoulder rush the option they would choose or would they try to break it with a weapon and keep some distance. You have now narrowed down the likely responses to something where they probably remain trapped. 

 That completely depends on what the enemy is. A horse would panic at being confined and would fling hooves at a dangerous looking steel cage, or bolt out of it. An intelligent humanoid wouldn't. An wizard with access to Misty Step most likely would simply teleport out of it. But generally most creature that find themselves confined will make some attempt(s) at escaping and especially during a combat situation are unlikely to just sit back and chill until they are released. Phantasmal Force is not Domination, the affected enemy can willfully do whatever they normally would do when confined. They can move as they will, they can attack as they will, they can speak as they will regardless of what the phantasm is. Since only the affected target can see the phantasm it the target has intelligent allies with them, most likely their first response will be to shout out "Help me! I'm trapped!" to which the intelligent allies will respond "No you aren't, there's nothing there, come help us kill these guys!" at which point most creatures are likely to attempt moving through the phantasm. 

If you want to restrain an enemy, use Entangle, or Hold Person, or Earthen Hand, or Web, or any of the other spells that actually conjure physical restraints. 

There are not specific rules for what Phantasmal Force can and cannot do, because that would completely destroy the creativity that makes the spell fun for both the DM and the players. Consider the following possible use cases:

1. Distract a guard dog by having it see a big pile of delicious meat at the far away from where the party is.
2. Lure a bandit away from their camp by having them see a lost chest full of gold coins.
3. Trick an enemy to stepping off a cliff with a phantasmal a bridge.
4. Scare off one or more harpies by creating the phantasm of the shadow of an Awk flying overhead.
5. Confuse/Distract a T-Rex by phantasming an attacking Triceratops right next to it.
6. Trick an enemy into falling off a tower by phantasming the ladder to the wrong location.

 As raw opinion is manifesting that says no moving of the phantasm some of your examples have trouble.

2 must be a very greedy and stupid, if gold dropped from air he wouldnt be a  bandit i mean you could try but there is no tell he wont investigate from afar or call a fella.

3 The cliff must be 10ft at most and unknown to victim. Cliff is too big to use smt like that propably a big hole or a crevice.

Number 4 could work if phantasm can at least move inside the 10 ft cube. Well that isnt specified as well, so i assume ppl who think it does not move must think it cannot even move in the 10 ft cube as well. How many turns would they be frustrated ? 1-2?  Will in their frustration fire back at your party? They can certainly do. bcs that will happen at most. phantasmal force cannot make you afraid.you spent 1 turn casting it so 0-0 at most...

Number 5 though yeah. it cant move bcs the triceratops is already large and you make a motionless picture of a triceratops so it doesnt move its head to hit the t rex propably the 2d8 of dmg is not from triceratops horns but from the sheer anomaly of what t- rex sees. By round 2 probably the t rex will move away anyway and there goes your spell.

Number 6 if he is stupid and lost the save you won if he is smart and was unlucky with the save he will use the ladder he remembers assuming he knows the tower. wouldn't you do the same?

I like phantasmal force and have tried stuff. this is what i get from dm's. lately i speak about them bfr i cast it which takes time and at the end of the convo im like yeah i cast hold person/flaming sphere. I think is meant to be an in combat spell that induces chaos to victim. in the dynamic place of a battle immovable 10x10 do most of the time nothing. 

Number 5 though yeah. it cant move bcs the triceratops is already large and you make a motionless picture of a triceratops so it doesnt move its head to hit the t rex propably the 2d8 of dmg is not from triceratops horns but from the sheer anomaly of what t- rex sees. By round 2 probably the t rex will move away anyway and there goes your spell.

Well the spell description specifically lists "creature" among the things you can create a phantasm of, and it says the target believes the phantasm. So a successful Phantasmal Force of an angry Triceratops is believed by the T-Rex to be living, real, angry Triceratops. Sure the Triceratops can't move to a new square, but the T-Rex with rationalize why it doesn't - e.g. it's in a defensive posture and is guarding a spot.

2 must be a very greedy and stupid

Have you met many gang members? Bandits are usually living outside the law off scraps in the wood just so they can steal money from people without having to do any work. Sounds stupid and greedy to me.

Number 6 if he is stupid and lost the save you won if he is smart and was unlucky with the save he will use the ladder he remembers assuming he knows the tower. wouldn't you do the same?

Not it is was a movable ladder, I'd assume someone had moved it when I wasn't looking. If it was stone steps I'd be more suspicious. 

I like phantasmal force and have tried stuff. this is what i get from dm's

That is the nature of these types of spells. Either you take away all creativity like they did to Command, and have specific mechanics the DM can't dispute. Or you leave it open ended and how useful something is becomes dependent on the DM. Good DMs are rooting for their players though and mine have always let me know if a creative plan I concoct would seem unlikely to succeed to my character who understands how the world works, before I try to do it. 

If we compare to other 2nd level spells... Scorching Ray deals on average 4d6 damage, Hold Person has 50% chance of doing nothing and at least 50% chance of not being usable at all, Flaming Sphere average 1d6 damage per round, Spike Growth deals ~6d4 damage, Spiritual Weapon deals on average 1d8 damage per round, .... the presented capability of Phantasmal Force seems very much on par with other 2nd level spells.