Brain Teasers/Riddles from the mind of the Frog

[Frog]

I've decided on making up some original riddles and brain teasers and seeing what the Gateway can do with them. There will be some riddles/brain teasers that will be taken from online, but adjusted. You won't find the answers online. Here's how it's going to work:

- I'll post up a riddle/brain teaser and you have to figure out the answer - simple enough.
- Post your answers here - still simple enough
- Once the riddle is figured out, I'll post up another one. If the riddle isn't figured out in a certain amount of time, I'll give the answer and post up another one. :)
- Edit: Don't be afraid to be wrong and post! :D
Let's start!

This one was done in chat, so it might be figured out quite quickly if someone knew how it was done. The style isn't original, but it works.

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Take a second to view the sequence of letters. Which letter should come next?

T X E S D L R F H Y S U F W E Q E D W J O X D E A P ?

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Good luck! :D