So I might get a chance to try out a College of Spirits bard in an upcoming campaign, and I have a question. Can someone walk me through the 14th level ability, Mystical Connection?
I get that the Tales from Beyond ability works like this:
I use a Bardic Inspiration die, roll it, and get the result that comes up on the chart. (this means that as I go up in levels, I get chances at more and different effects)
But the Mystic Connection ability says:
"Whenever you use your Tales from Beyond feature, you can roll a d6 and use it instead of expending a Bardic Inspiration die. You still use your Bardic Inspiration die for the tale’s effect, without expending it."
These two sentences seem at odds to me. The first one says that instead if using up one of my bardic inspirations, I just get a free 6d to roll (so infinite use, but low level results) 
The second sentence seems to say, just go ahead and use the power with your current die, but don't use up any inspirations (infinite use, high level results)
I am not getting what they are saying. Help.

It looks like a case where the rules were changed late, and some awkward wording got missed in an editing pass.

I interpret it to mean "You use, but do not expend, your Bardic Inspiration die" for the roll. 

(If I were to guess, either Mystic Connectiom used to be a flat d6 or it used to start higher than your base BI die. Now it's redundant because Bardic Inspiration is always at least a d6.)

The wording is a bit clunky but I'll try to explain it.

"Whenever you use your Tales from Beyond feature, you can roll a d6 and use it instead of expending a Bardic Inspiration die. "

This means when you want to use the ToB feature instead of rolling your Bardic Inspiration for the Tale and expending it, you can instead choose to use a D6 and don't expend a bardic inspiration die. This means you can use it as much as you want but would be limited to the tales: Beast, Warrior, Friends, Runaway, Avenger, Hero.

Note this is for choosing "which Tale", and not "rolling as part of the Tale's effect."

"You still use your Bardic Inspiration die for the tale’s effect, without expending it."

This is referring to the tale's effect for the Tale your d6 got you. By 14th level your bardic die is a d10. So if you used ToB you'd roll the d6. Let's say you got the Hero tale.

Hero. You speak the tale of an epic hero. Choose a creature you can see within 30 feet of you. The target gains temporary hit points equal to a roll of your Bardic Inspiration die + your bard level. While it has these temporary hit points, the target’s walking speed increases by 10 feet.

So you can choose your target and then roll your Bardic die, a d10. So this might be, say, 6. That target gets 6 + 14 = 20 temporary hit points and their speed increases 10 ft while they have them.

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d6 = determines which Tale

Bardic Die = when needed for the Tale's effect.

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Hope that makes sense.

YES!  Thank you Cyb3rM1nd !!! Now I get it.