When I draw from the Wondrous Item Deck of Many Things, am I and the rest of my party made aware of its effects? For example, if I draw the Rogue card, do I know that someone (currently undisclosed) now has enmity towards me?
[RPG] Are the Deck of Many Things’ effects known to the drawer
dnd-5emagic-items
Related Solutions
What you posit is reasonable except for one thing: The Deck of Many Things has a random outcome that the DM determines by a die roll.
As a magical artifact, I would say that it consists, as a whole of the cards it contains, not of a bunch of independent magical cards. The whole Deck itself is the magic item here, not the cards themselves, they are just pieces/components of the larger artifact. So the individual cards do not necessarily have an independent existence outside of the deck, nor any independent, fixed or specific order inside of it. When a character draws a card it is "randomly" determined by the Deck.
And this element of randomness is very important to the artifacts nature and being (in fact I would say that it is the central attribute of it). So, technically, the DM should re-roll the die if the draw/turn gets re-set, not just play it as though there now (or ever was) any specific pre-determined card on the top of the deck. (of course that's up to the DM).
Look at it this way: If a party engaged in combat resets the turn with Forced Dream, is the DM going to say that the turn gets played over, but everybody get's exactly the same attack and damage rolls as the first time? Or does the DM rule that everything has to be re-rolled fresh and as it happens? My guess is most DMs would say the second, both for combat and for the Deck. Which means that while Forced Dream could be used to avoid a bad outcome from the Deck, it could not be used to then force that same bad outcome on someone or something else: it gets a new random roll.
You should only get as many cards as you declare - three
The character being removed from the deck's presence opens up some some cause and effect chains, but it is the two remaining cards (not yet drawn) that erupt after the hour, not "the whole deck unleashes at once" as stated in the question's text.
Three cards should get drawn, but the last two may not be usable
If you fail to draw the chosen number, the remaining number of cards fly from the deck on their own and take effect all at once.
If you declare three, and you only draw one, then after an hour the other two cards come out of the deck and take effect immediately. The text does not specifically state "the whole deck," so this reading of that description makes the most sense to me.
That doesn't completely solve the conundrum. The DM will need to make a ruling on which card takes effect first, but the description suggests that you aren't drawing the cards at this point: they are being drawn for you by the magic of the deck. Let's call that "autodraw."
The above 'draw no more cards' lacks a card drawing character, but it leads to some other "how does this work?" questions for the DM to resolve.
Example based on your scenario:
First card: Jester (yay, XP for you)
Fail to draw, so one hour later ...
Second Card (autodraw): Donjon (you are trapped!)
Third Card (autodraw): The Fates (you can undo Donjon1, lucky you)
or
Third Card: Balance (you are trapped and you change alignment).
or
Third Card: Knight (The DM may rule that he appears wherever you are trapped, so maybe he can help you get out1, but he may appear where the deck is and where you are not).
1 What suspended animation means, for this result, isn't explicitly spelled out
Donjon. You disappear and become entombed in a state of suspended animation in an extra-dimensional sphere.
We can get an idea from the Astral Projection spell description (PHB, p. 215):
... the material body you leave behind is unconscious and in a state of suspended animation; it doesn’t need food or air and doesn’t age.
The Sequester spell description (PHB, p. 74) says for suspended animation ...
"Time ceases to flow for it{what's being protected by the spell} and it doesn't grow older."
It appears that you'd be awake, and maybe able to communicate with that Knight, but the DM may rule otherwise. (For example, the DM may rule that the Knight pops into existence where you are as you pop into that other place).
Which spell description's sense applies? DM ruling needed here.
Best Answer
The Deck of Many Things is a Legendary, Wondrous Magic Item.
The Arcana skill is written as follows (Emphasis Mine):
You simply need to roll a knowledge check against your Arcana skill. It will be up to GM discretion whether or not the roll applies to the whole deck or to each card you draw. You will also have to talk to your GM and decide between you whether or not it is reasonable for your character to have prior knowledge of the deck given their background, as the Arcana skill states only that it allows you to recall the information, not to suddenly figure it all out on the spot.
If you decide that your character did not have reasonable prior access to this knowledge, you may be able to, at a later time, study the deck to gain this knowledge.
But, if you decide your character did indeed have prior knowledge of the deck, and you pass the roll, your character will recall the effects of the Rogue card and know that somebody is out to get you, though you don't know who.
If you fail the roll, your character draws a blank and can't remember what the card does.