I just beat Elektra on what must have been my 10th try. I got a lucky board and denied red and black most of all. What really helped was letting her use her Purple so I could strengthen those tiles.
I got a Red Hulk cover-which I have my my championed Red Hulk and then got another LT. I opened that and got a Red Spider-Gwen.
beat her on the second try... I got lucky and was able to stay inviso while letting her match purple to make me tiles, then had a nice cascade to strengthen my tiles a few times the first turn.
got a green black bolt cover for my troubles... wish I could get his charge tile power