This is Nathan/Nate/N8 (or, rather, his Tumblr). You're probably here because of my really bad MS Paint Nuzlocke comic using probably-stolen photos. Welcome!
What Generation were Pokemon introduced that got mega evolutions? (including unreleased Pokemon)
Generation 1: 13 Pokemon (Charizard and Mewtwo only counted once)
Generation 2: 6 Pokemon
Generation 3: 20 Pokemon
Generation 4: 5 Pokemon
Generation 5: 1 Pokemon
Generation 6: 1 Pokemon
What types are associated with Mega Evolutions?
Grass: Venusaur, Sceptile, Abomasnow
Fire: Charizard X/Y, Houndoom, Blaziken, Camerupt
Water: Blastoise, Slowbro, Gyarados, Swampert, Sharpedo
Psychic: Alakazam, Slowbro, Mewtwo X/Y, Gardevoir, Medicham, Metagross, Latias, Latios, Gallade
Poison: Venusaur, Beedrill, Gengar
Flying: Charizard Y, Charizard X (lost), Pidgeot, Pinsir (gained), Gyarados (lost), Aerodactyl, Altaria (lost), Salamence, Rayquaza
Ghost: Gengar, Sableye, Banette
Normal: Pidgeot, Kangaskhan, Lopunny, Audino
Bug: Beedrill, Pinsir, Scizor, Heracross
Dark: Gyarados (gained), Houndoom, Tyranitar, Sableye, Sharpedo, Absol
Dragon: Charizard X (gained), Ampharos (gained), Sceptile (gained), Altaria, Salamence, Latios, Latias, Garchomp, Rayquaza
Rock: Aerodactyl, Tyranitar, Aggron (lost), Diancie
Fighting: Mewtwo X (gained), Heracross, Blaziken, Medicham, Lopunny (gained), Lucario, Gallade
Electric: Ampharos, Manectric
Steel: Steelix, Scizor, Mawile, Aggron, Metagross, Lucario
Fairy: Gardevoir, Mawile, Altaria (gained), Audino (gained), Diancie
Ice: Glalie, Abomasnow
Ground: Steelix, Swampert, Camerupt, Garchomp
Long story short, we should be encouraging more mega evolutions from later generations and of Ice, Normal, and Ground types.
Updated with the most recent leaks. Still hurting for Ice types.
Updated with Gallade, Sharpedo, Camerupt, Rayquaza, Beedrill, and Pidgeot.
Updated with Steelix and Glalie. Hooray for an ice type! Currently, Ice and Electric have the fewest Mega evolutions.