nedoking

Well, to make it short - we ended up removing Flash and replacing it with Darkness.  His concept was a "puff of smoke" that left his target blind.  I explained that was NOT Flash.  It last only last 1 phase so it got a Limited Power.  It is LINKED to his Teleport and he MUST use it with teleport.  Also purchased was Personal Immunity.  I must confess that I am still thinking about Trigger.... both seem right... I guess the question is "Advantage or Disadvantage".
 
Se he can teleport to a target, the Darkness activates, he can see, his opponent cannot (usually)
 
Hah - kinda funny - this character WOULD leave you in the dark!   🙂
 
 
Again - thank you to all who offered their thoughts.  This is a SUPER community!

Well? What did you decide? Don’t leave us in the dark! 😀

*BAMF*
"My eyes!"

Again - many thanks.  I just completed a long character build session with the player - and we both finished happy with the result.  I think it will be balanced and a blast to play. 

That is my interpretation as well.

Perfectly legit interpretation, although I will note that Pepper Spray is a sample Flash power in 6e, and I am pretty sure I saw tear gas and sand in the eyes as Flash Attacks in prior editions.

This is possible, using a variety of different mechanics, but each has its own costs, much like the Trigger advantage here, to avoid using an Attack action (and ending the character's phase) to use the Flash.  Nothing in Linked removes that requirement.  If the Flash is Linked to Teleport, it can only be used when the character Teleports.  He still needs an Attack action to use the Flash.  If Teleport is Linked to Flash, then the Flash attack must be used (requiring that Attack action) for the character to Teleport.  Here, Teleport Linked to Flash and Flash with Trigger Linked to Teleport would be my approach.  NOTE:  Pretty sure 4e Linked required both abilities to be used, or neither.
 
 
That comes down to power definition - I'd say the arrival location, as that seems to be the power envisioned, but the departure hex would be fine for a Triggered Flash as well.  I would not allow both (at least not without an added advantage).
 
 
Combined Attacks are what I think you are envisioning (6e terms - 4e terms may have been different, such as "Multiple Power Attack").  Both Combined and Multiple Attacks have their own restrictions, but are other means of having two or more attacks go off in the same phase.  Neither would allow the Flash if the character makes a full move, rather than a half move, with the Teleport as an attack action would still be required. 
 
As a combined attack requires attacking the same target, and the Flash is envisioned as AoE or Explosion (targeting a hex), the character's other attack would also have to target his hex.  So that's out.  A Multiple Attack requires a full phase (not sure we had Rapid Attack in 4e to cut that down to a half phase), so the character cannot Teleport and Multiple Attack. It also imposes OCV penalties and halves DCV.
 
 
A crucial issue - regardless of how it is built or what it costs, will the "move and blind" be problematic in the game? I suspect the game will evolve to have a lot of opponents with enhanced senses, minor Flash defense or other means of getting around this ability.  If that results in the ability rarely or never being useful, the player will reasonably be unhappy at the points spent being useless.  If the ability becomes an "autowin" button, the detriment to the game is pretty obvious.  Striking a balance is the key, and it may take some time (and some in-game frustrations) to find that balance.
 
 

And you can do a Mutli-Attack now (is that the right name.) Which was claimed that that was always an option-as long as you had the END. So it not really an argument is it?
Nedoking, the biggest thing is whether or not the build is legal by RAW but rather does it overly unbalance game play? Just because it LS “legal” doesn’t mean that the GM has to allow a certain build in the game.

Use Trigger.  If the Teleport is always accompanied by the Flash, put Linked on it as well.

So I should just Link one of my attacks to Running, always move at least 1-2 meters (in D&D, a 5' step), have that Linked attack go off automatically, then use my normal attack?
 
Linked is, by default, a one-way street in 6e.  You MUST use Power A to have the OPTION of using Power B.  If the Flash goes off only when teleporting, and goes off every time, that plus the drawbacks of being forced to Flash every time would justify a Linked limitation on both powers, at least in my opinion. 
 
All of the drawbacks you suggest for Flash also apply to a character with a standard Flash Attack.  Flashbulb is aiming at me?  Quick, cover my eyes!
 
"OK guys, everyone hold your action until Flashbulb aims at the Big Bad - then, when he covers his eyes and is blind, blast him at half DCV."
 
By the way, what if the SFX of his Flash + Teleport were a puff of smoke stinking of brimstone, which irritates the eyes of those exposed to it, instead of a blinding light?  "I'll cover my eyes" seems like a drawback of selecting the SFX of a bright light rather than irritation to the eyes, much like most knockout gases in early editions moved towards being skin-absorbed rathet than inhaled to require a higher level of Life Support to defend, and avoid "I hold my breath".
 
As to being obvious, a normal Flash is also obvious.  And isn't Teleport a Visible Power anyway?

I just read Linked in 4th and the closest it says it that “If two powers are Attack Powers then they go off simultaneously”. I suspect the reason why you find a qualifier in 5th because in 4th, Linked is a little grey and hence why the OP’s question. And I can see why a GM might rule otherwise.

Good points. Consider though that if you Flash every time you T-port you will be noticed. No sneaking from that! Also consider that Flash can be defended against if someone is prepared. The old cover your eyes trick. So how long would it take for a smart villain to do that? Also Flash Def is fairly common too. I think this balances out the free attack from it being linked. 

I reviewed 5ER and 6E Linked and don't see anything indicating that it makes an Attack Action a non-Attack Action.
 
Yes, Linked does reduce utility so it's a Limitation... but changing an Attack Action to a non-Attack Action is an Advantage.  And Trigger explicitly does just that.

I don’t have access to my books so cannot look up the specifics in 4th edition.  But considering the rules have not really changed that much the fact the latter editions clearly state that are indicative that it is true.  Most changes between editions are more about new rules or adjusting the cost of a power or modifier.
 
One of the fundamental rules in the game is that if a limitation that does not limit you it is worth no points.  That rule went all the way back to the original game.   While it is not actually stated that also means that an advantage that does not increase the power is no advantage.  
 
Trigger is an advantage because it allows you to create a situation where you can setup the power in advance.  This means the power with trigger is more useful than one without, so you have to pay more.  On the other hand, linked reduces the utility of the power so you pay less.  I am going from memory but if I remember correctly in 4th edition when you used linked power, they always went off together.  Even if I am mistaken about not having the option it is the default.
 

Do either of you have a cite for that?  I re-read Linked and don't see anything indicating that it makes an Attack Action a non-Attack Action.
 
I thought Trigger would be the way to go... but there's also no text in 4E indicating that it makes an Attack Action a non-Attack Action, either.  Although I would allow it.  5ER specifically addresses this, "...even if activating the Trigger involves an attack or making an Attack Roll, it does not constitute an Attack Action (unless the GM rules otherwise)." (p. 270)

I’m almost positive that Personal Immunity is in 4th Ed. Good call on No Range.

Ninja-Bear is correct by linking the flash to the teleport it means it does not require an attack action. 
 
In addition to linked you should also take no range, and maybe personal immunity.  Not sure if personal immunity was in 4th edition, but if it is fits.

As far as I recall, if you linked Flash to T-port then the Flash wouldn’t end your turn. You should still be able to attack if you T-ported.

Trigger is indeed in 4th Ed.

Depends on how the GM interprets the power. But, well...
Yes it does. In 4ed unless the attack is Linked you can only do one attack and the phase ends. Question: can he teleport without using the Flash attack, or must he always Flash?
Trigger. I don't remember if the advantage was in 4ed or not. In your example it would be Trigger (when arriving from a Teleport by own power). 
 

The "does damage to others when teleporting" thing is tough, as is the "grab and teleport away" but it can be done with a few tricks including stuff like trigger.  Nightcrawler has a VERY high speed, around Spider-Man level (7 or so?) because he's doing like 3 things to every agent's 1.  He's incredibly agile and can blend into dark places, making him difficult to see.  He's got a lot of training in fencing and knife fighting as well.

If I had a player routinely using a tactic like this, I would be inclined to flesh out how it will work.  Perhaps the NPCs make PER rolls opposed by Nightcrawler's DEX roll to notice his last-minute disappearance before attacking/pulling the trigger.  Even trained (agent-level or higher) soldiers will find this difficult given Nightcrawler's agility, and that is probably fair.  Then we need to figure out the OCV of the shooter (0, since he was not aiming at his teammate?  Is it a surprise move if the target misses an opposed roll with Nightcrawler?) and DCV of the target. We also need to assess whether this becomes more predictable with re-use on the same opponents, if opponents have been briefed on Nightcrawler's tactics or even if this tactic becomes more broadly known due to media coverage of Super-battles where it is used.

So I was re-reading 5E Champions.  In that book this tactic is called a "Sucker Attack".
 
I won't reproduce the text.  The technique is to get between two enemies and wait for one (or both) to attack.  The character must have a Held Action, then Dodges (Nightcrawler would of course bamf out).  Make the normal DEX vs. DEX roll to go first; if the dodger loses the first attacker's attack happens before the dodge (rather than the normal 'Abort to a defensive Action automatically goes off first', but this is an offensive use of Dodge and so seems reasonable).  If the dodger wins the contest, the attacker makes an Attack Roll using only OCV (no CSLs, maneuver bonuses, or suchlike) against the second attacker's DCV.
 
Aaron Allston had it figured out in 2002. 😁

To me, that's a tactic Nightcrawler uses, not a power that he has.  I think you have it right - he teleports between two NPCs and bamfs out as they attack.  The effectiveness depends on the NPCs.  Are they trigger-happy?  Probably works.  Are they trained soldiers?  Probably won't work (maybe the first time...)

We can build a lot of different things.  This could be a complex build involving Triggered attacks (perhaps an area of effect attack with a trigger and some limitations; it doesn't really matter if the SFX of the attack hitting the two mooks are identical to their own SFX). It could be a Change Environment that reduces the mooks' DCV against the cross-attack.  Note that Nightcrawler only seems to use the ability against mooks, so it doesn't need to do a lot of damage - point out that he doesn't use this against Magneto or the Brotherhood of Evil Mutants.
 
My guess is that this ends up being a very complex build with limited practical application, and is best left to writer's fiat as Mr. R said, though.  In fairness, that writer's fiat is also not how gamers normally play.  "What? He vanished at the last second? Well, I don't attack then, realizing in a fraction of a second that I should not fire that blast after all."  Maybe that CE imposes a (penalized) DEX roll or the target fires off their most readied attack.