I've yet to see Medicham give a strong performance, outside of a few specific matchups such a Night March where it can take multiple Prizes. That aside, with only 90 HP and requiring two energy to attack (Celebi isn't in Standard and Shrine of Memories takes away the damage from Fighting Stadium), Medicham tends to not hit hard enough to make important KOs. As far as other Fighting decks go, I'm seeing Dugtrio from XY as a strong contender. Combined with Eeveelutions you can exploit a lot of weaknesses. However I feel the days of EX-hard Fighting decks are behind us. Focus Sash is a neat card, but it can be removed with Xerosic, a card that I've managed to squeeze into every list I've built.
As far as Night March goes, while still a strong contender, the enemy here is consistency, not power. Mew allowed for some clutch plays that just can't be followed through in the same manner, and makes prizing Night Marchers even more troublesome. Yes there are a few workarounds like Bronzong, but they are not without drawbacks.
Yveltal is just too powerful of a card to disappear completely. Partnering with non-EX attackers and clever techs has been a proven way to deal with its weaknesses. Zoroark is capable of doing some real damage with the right setup, and makes for a good partner. Standard Yveltal decks will have a very different structure from what we've seen in the past.
This applies to both Standard and Expanded, but I think the biggest killer of creativity is Hex Maniac. This can come out of nowhere and lock all Abilities at the worst possible moment for your opponent, and many lists are running more than just one. This can make decks that rely heavily on Abilities risky, as some can become crippled if they have even one turn without their powers. Imagine yourself playing an Aromstisse deck. Your active Pokemon has a precious Rainbow Energy on it, and your opponent uses Hex Maniac, then attacks. You're in a pickle. If you don't use a Max Potion, your Pokemon will be knocked out. You can't Fairy Transfer, so if you heal you can kiss your Energy goodbye. This is just one scenario where a random (or should I say well-timed) Hex Maniac becomes more than just a minor annoyance. Decks that's perform well will be those that are not overly reliant on their Abilities.