Under Control

Items on this page with a purple dotted border are affected by what Matt and Emma have done up to this point. Because they haven't gotten here on this timeline, these items are currently undefined.
This puzzle is interactive, or otherwise solvable only when logged in with a team.

Lucy says she's got things under control, but she still needs Matt and Emma's help to restore the life support.

Yellow hexagon
Triforce symbol
Black circle
[See puzzle page for additional images.]
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Matt says
3 of the 4 letters are in the first half of the alphabet.
Emma says
These letters are all different letters in my favorite U.S. national park, which is known for its buttes!
The uppercase missing letter contains a vertical line.
Lucy says
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Matt says
None of these letters are on the bottom row of a QWERTY keyboard.
These are all vowels.
Lucy saysEmma says
If I added eyes, the missing letter could be a happy face!
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Multiple of these letters are Roman numerals.
Lucy saysEmma says
The missing letter is in the first 5 letters of the alphabet.
Matt says
The missing letter is an odd prime with A1Z26.
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Emma says
The missing letter is one away from an existing letter, using a Caesar shift.
The Caesar shift is backwards.
Lucy saysMatt says
The uppercase missing letter has all straight lines, but no right angles.
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These letters are all pentominoes.
Lucy saysMatt says
The missing letter is a multiple of 4, using A1Z26, that isn't already used here.
Emma says
None of these uppercase letters have rotational symmetry.
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Emma says
Old MacDonald sings about the missing letter.
One of the letters is repeated.
Lucy saysMatt says
The letters together do not spell out a U.S. state.
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The missing letter is a vowel.
Lucy saysMatt says
These are 4 out of the 5 letters I use in my Wordle opener.
Emma says
Matt uses a bird for his Wordle opener.
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Matt says
If you add "i", the letters spell a verb.
The verb is present tense.
Lucy saysEmma says
The verb is related to eating.