I like the thread, and have therefore decided to comment on each of your points in an orderly fassion.
Marvel team up: I was kind of disappointed since none of the new characters in Dark City had multiple affiliations. However, there could be a mechanic that allows a character to temporarily gain an affiliation of another character that was played that turn. I don't necessarily think this is a great idea, but don't see anything wrong with it either. I would prefer that over time we received multiple versions of heroes for each afiliation than see a single card with multiple affiliations. I do like the idea of changing card affiliations though.
Speedy: Fast characters that can perform his/her ability an X number of times in a turn and spends the X number of turns to the side before it is put into the discard pile. One thing I don't like is when you have to track multiple different cards' abilities. Trying to remember how many turns a card has been to a side could get annoying. Your idea gave me another one though. Same key word, but different ability. You may discard 2 hero cards from your hand to draw a card that you have already played this turn back into your hand that has the keyword, Speedy. Quicksilver, for example, could have a card that does 2 damage, and could then be playe multiple times in a single turn if you keep discarding cards. On a normal hand of 6 cards, you could then play him 3 times in a single turn.
Ko Pile Manipulation: This was one of the things I mentioned in my last post…still waiting.I'm waiting with you.
Stalker: A hero that can be put into a space in the city and wait for a villain/bystander to show up. If the space is empty and a bystander is flipped it is automatically rescued and the hero is put into the discard pile. If it is a villain, and that heroes attack is equal or greater to the villains cost it is defeated automatically negating its ambush effect if any. I don't like this idea because it is one extra thing we have to track. In this case, it is who's card is it?
Insert name here): A card effect similar to a villain’s ambush affect but for heroes when they are flipped into the HQ. This affect would be positive and help all players.I honestly expected we would see something like this in the LDC expansion. Awesome idea.
Sacrifice: Hero KO’s itself but has an over the top, powerful ability.This seems like a no brainer, surprised it still isn't in the game.
Stockpile effect(I gave it a lame name in the last post): Hero is set to the side and gains a counter (the card has a cap limit for counters). Remove X counters do X. The character is discarded when it has no counters on it. I don't like this idea, because it is an extra thing to track. Will then have to have counters involved as well. I don't like overcomplicating games.
Character specific interactions:EX: Cloak + Dagger: Dagger could gain teleport if Cloak is revealed in hand, alternatively Cloak could gain some extra attack strength if Dagger is played. [/q]
Not sure if this would be a great idea but it would surely up the thematic element. Some Heroes/Villains have special relationships and it would be great to highlight this within Legendary. The characters could get an extra bonus if their counterpart is played during the same turn.
I've stated elsewhere, in a custom card deck version, that i don't like this type of idea at all. When you randomising heroes, the chances of the 2 heroes that would compliment each other is just too low. What ends up happening is they are either too expensive to have their worth if you only have one in the deck, or too cheap for their worth if you have both in the deck.
I would prefer if mechanics that came out that causes heroes to work while together, without relying on specific names being used.
For example, Cloak could have an effect that says that if you discard a card that costs 3 or more, you may do a certain ability. And then a Dagger card could say that if you have to discard it for some reason, draw it back into your hand. The Cloack could work with any combination, and the Daggar would work well with many combinations, but together, they do get a certain synergy.
I also think a new mechanic that should be added is a card that can be played when it is not your turn, to help team-mates, or to hinder them. A card that you can either play on your turn to get the ability, or a team-mates turn to add or reduce the same amount. This would be in theme of many of the darker more selfish orientated heroes.
My 2c is over.