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If an obstacle is removed, how fast does TFD move to catch up to its caster?

...follows you so that it remains within 20 feet of you. (PHB 282)

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    \$\begingroup\$ I'm not sure why this was unmarked as a duplicated. It's the exact same question as at Does this Tenser's Carnival Attraction gimmick work?, just with a less fancy title & example. Both are asking (and only asking) how fast the Disc catches up to the caster after an obstacle is removed. \$\endgroup\$ Apr 5, 2018 at 17:26
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    \$\begingroup\$ @SevenSidedDie I unmarked it because it's a far, far less convoluted situation. Someone looking for "so I remove the obstacle, what's it do now?" shouldn't have to expend effort trying to understand a theoretical carnival ride and what it does and how the answers about what the carnival ride does relates to an ordinary situation. \$\endgroup\$ Apr 5, 2018 at 18:15
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    \$\begingroup\$ @doppelgreener Probably the other should be a duplicate of this one then? They're identical problems — this one has a simpler, more accessible description though. \$\endgroup\$ Apr 5, 2018 at 18:42
  • \$\begingroup\$ Is linking the pertinent information in the other question and vice versa an option? \$\endgroup\$
    – Digcoal
    Apr 5, 2018 at 19:10
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    \$\begingroup\$ Voted to leave open in review for the reason explained in doppelgreener's comment above. \$\endgroup\$ Dec 23, 2021 at 17:27

4 Answers 4

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It catches up "immediately"

This question is essentially unanswerable, because D&D 5e doesn't have any explicit concept of velocity to begin with. While characters have a "speed" stat, mechanically it is just the quantity of movement you have available to use each turn. From a mechanical perspective, using that movement on your turn is effectively instantaneous. Similarly, the rules for how fast you fall, given in XGtE, don't specify a speed; they specify that you fall 500 feet at the end of each of your turns. Again, this movement is effectively instantaneous: you spend your entire turn at one fixed location in the air, and then at the end of your turn you instantly descend to your new location 500 feet down.

To put this another way, ask yourself: if nothing is in your way, what is the difference between walking 30 feet and teleporting 30 feet? Mechanically, it turns out these are almost identical. The main difference is that walking requires a clear path and can provoke opportunity attacks or trigger other effects along that path. Other than that, there's really no mechanical distinction: either way, you simply arrive at your destination.

So, in the same way that all of the "normal" movements mentioned above are instantaneous, Tenser's Floating Disc also moves instantaneously as soon as an obstacle is removed. And like the above movements, this doesn't mean that the disc literally moves at an infinite speed, just that mechanically speaking, the movement happens all in one "step". Ultimately no speed is specified, and nothing in the rules can help us infer the speed because "speed" (in the sense of a rate of change in position, not the game term) largely doesn't exist as a concept within the rules of D&D 5e.

As for the actual speed, Gamebuster19901's answer gives us a reasonable upper bound based on the maximum linear distance the disc can possibly travel at once (80 feet) divided by the duration of 1 round (6 seconds). However, after removing an obstacle and allowing the disc to travel that 80 feet, the caster can then use their own movement on the same turn, causing the disc to continue following them and move even further. So it is not terribly difficult to make the disc move 140 feet in a single turn just by taking the dash action. Even longer distances are possible if one has a speed greater than 30. So in practice the disc's maximum speed is only limited by the caster's. As long as its path is not blocked, the disc keeps up with the caster, trailing 20 feet behind them.

In addition, as Tenser's carnival attraction shows, there are extreme edge cases where the disc could potentially be forced to take a much longer roundabout path because the direct linear path is blocked. The spell's text simply doesn't specify how the disc handles such cases. As with many things in 5e, the rules cover the common cases and it is the DM's job to fill in the rare edge cases.

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PHB 181 states

"In situations where keeping track of the passage of time is important, the DM determines the time a task requires.

...

In combat and other fast paced situations, the game relies on rounds..."

Assuming an unobstucted path, and that the disc moves at a specific place in initiative, the disc can only move a maximum of 80 feet per round, because the spell ends when the caster is more than 100 feet away, and it will stop moving when it is within 20 feet of the caster. (\$100-20=80\$).

If the DM rules that the disc always moves at max speed, then the speed of the disc would be 80 feet per round

\$\LARGE\frac{80\text{ feet}}{1\text{ round}}=\frac{80\text{ feet}}{6\text{ seconds}}=13.\overline{333}\text{ feet per second}\approx{9\text{mph}}\$


If rounds are not used to resolve this, then the speed of the disc is infinite, and it cannot ever be more than 20 feet from the caster if its path is unobstructed, unless the caster is teleported.

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    \$\begingroup\$ What happens if the caster can move more than 100ft in a round? \$\endgroup\$ Dec 25, 2021 at 19:45
  • \$\begingroup\$ Exactly what the spell says it does? The spell ends if the caster moves more than 100 feet away. \$\endgroup\$ Dec 25, 2021 at 22:50
  • \$\begingroup\$ So are you saying the disk only starts to follow you after your movement is over? \$\endgroup\$ Dec 25, 2021 at 23:03
  • \$\begingroup\$ I believe it would ever occur immediately after the caster stops moving. Like most other environmental effects, it would be up to the DM, but it should move at the beginning/end of the round, or at a specific initiative, or at the end of the caster's turn. \$\endgroup\$ Dec 25, 2021 at 23:10
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    \$\begingroup\$ There's nothing in the spell's text to suggest that the disc "waits" for the end of your turn/move before following you. \$\endgroup\$ Dec 26, 2021 at 13:29
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There is no guidance in the Tenser's floating disk spell description as to how fast a disk that has been prevented from moving to get within the 20' maximum range will move if it is no longer prevented from moving to be within 20' of the caster.

The disk is immobile while you are within 20 feet of it. If you move more than 20 feet away from it, the disk follows you so that it remains within 20 feet of you. It can move across uneven terrain, up or down stairs, slopes and the like, but it can't cross an elevation change of 10 feet or more [...] If you move more than 100 feet from the disk [...], the spell ends.

Thus it's up to the players (especially the DM) to decide what they think is the best option.

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What is the tractive force of Tenser's Floating Disk?

This question was possibly answered here, although it's not quite what you are looking for. In 5E the speed of Tensors disc is not specified. If you use 3.5 rules it's capped at the normal speed of the caster.

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    \$\begingroup\$ In 5e it theoretically can move 80ft in a single round as it moves until it is when 20ft of you. .. no speed limit is given \$\endgroup\$
    – Pliny
    Apr 12, 2018 at 20:52
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    \$\begingroup\$ I don't think maximum distance per round is the same type of speed OP was asking about, bu yes, correct. \$\endgroup\$ Apr 13, 2018 at 16:16

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