Elektra's DDQ opponent: Blade!

Daken - Very Hard.
He heals on every turn. While there is a chance that he might do some self-damage if you can really control the on the board, he's still gonna heal way more often than not.
Those tiles. Not only will he drop two on every green match made by anybody, they will be scaled to 270 AND they drop on Red leaving Ballet of Death extremely vulnerable. On the flip side, Double-Double Cross can help negate some of that BUT you are adding fuel to his fire because...
his is already one of the most spammy skills in the game. Scaled to 270, the hits will be big and will be often. By denying blue, this can be mitigating, but he's going to get a couple off in a match and they are likely to hurt.
Daken can be beaten by Elektra, but it will be an extremely challenging fight. Anyone with less than 5 covers is going to really struggle.

Daredevil - Rage Quit Hard.
Any character that can stun should be forbidden from being an opponent in 4*DDQ. Especially Daredevil, who only has to fire it once to be extremely effective 1-vs-1. On the plus side, the AI is really pretty stupid and often matches off their own CD tiles, but even then he gets 3 back in the process. Daredevil is a very strong 3* character. At level 270, he can take on any number of 4* characters of equal level successfully. Facing him with Elektra would feel very similar to how facing Cyclops was with XFW.

Punisher - Moderate.
Punisher gets slept on. Even as one of the old guard of MPQ 3*'s, he's still a very serviceable character. Scaled to 270 he is lethal. While none of his skills are overwhelmingly dangerous by themselves (unless your health is under 40%), they are all low cost and spammable.
His drops a countdown tile, potential a problem for Ballet of Death. He drops & on basic tiles, any of which could be or , another problem. And his board shake also presents an issue. The tiles can be stolen, so that can ease some pain, but everything he does will continue to aggressively eat away HP. I don't think this is an impossible fight, but it ain't gonna be easy. Elektra has to get that rolling quick and keep it up the whole way.
That said, I believe he is beatable if Elektra can get the right skills off at the right time.

Bullseye - Easy.
Bullseye would be a very easy opponent to down. If he is indeed the opponent for Elektra, thank the Devs for a very nice gift. His is reliant on there being special tiles on the board. So both 's wash each other out.
His is not effective until after someone has been downed. This skill becomes meaningless in 1-vs-1.
That leaves his . This skill will do good damage at 270 and will potentially create cascades that could include criticals. Deny , drop , drop , game over.
Personally, I am praying that Bullseye is the opponent. Note - if he is, you can practically guarantee that his teamup will GSBW .

Kingpin - Very Hard.
Kingpin's , drops CD's. Lots of them. Good, those can be dealt with via matching them away. At least a little bit. Some of them drop to steal. Also good. They do A LOT of damage. Bad. He can fire it fairly cheaply. Also bad. They drop on tiles. More badder.
His creates for him and steals his opponents strongest color. Ok then. Good news here is that Elektra's strongest color is , not or . But we need that purple to steal those strike tiles. And this skill is also pretty cheap to fire.
And lastly, his chief skill, You Got Fingered , does big damage WITHOUT any CD's on the board. With them, it's straight up lethal.
Kingpin is one of the upper tier 4* characters. He doesn't show up in the meta very much, but if you have him max-covered and leveled, I'm sure you use him for lots of things and extremely effectively. Elektra is so outclassed by KP that it hurts. And so would this fight.

Blade - Very Hard.
Blade's can be stolen. That helps. But they also overwrite Ballet of Death and they will pop up fast and furious.
The number of strike tiles on the board impacts his , whether they are the cheap ones Elektra drops from thieving them or the stronger ones he drops on his own. If he gets off a purple, the fight is probably already over, unless you can match them away quickly and easily.
His will do minor upfront damage and then be stealing , feeding into his skill that will kill you. None of that is good. Denying & will be off maximum importance in this fight.
Whatever the case, Blade is also an absolute top tier 3* monster. He puts the hurt on at level 166. At 270, forget it.

Psylocke - Easy.
Psylocke would be an interesting matchup and probably pretty easy to deal with. Psylocke is better than she gets credit for, but she relies on being a part of the right time and she specializes in taking down opponents with low HP.
Her drops . Those can be stolen, but again, they drop on creating an issue for Ballet of Death.
Her would not be an issue in most cases. It's a long CD tile, it steals from one color that you have the most of. In a 1-vs-1 fight, this could be a problem because you are playing the denial game. Considering & are competed for colors, it might not go well. But in my experience, I have never faced this skill and had an issue with it.
Her is probably the most dangerous. It's cheap, it drops which are a real problem to deal with in these kind of fights, and it drops them on other . Plus, at 270, she will drop some strong ones.
Even after considering any of that, Psylocke should be an easy opponent for Elektra to deal with, provided she has enough HP to withstand a few tiles on the board.