Here's my notes on the Kanto region Mega Pokemon.

Mega Venusaur: A kind and gentle soul, Megasaur always takes care of their partner during the long grass type mating sessions, it's fluids thick and sweet like tree sap. It grows juicy fruits during mating and feeds them to their mate, keeping them fed and hydrated. The fruits also enhance sensation, so you can stay sensitive and enjoy even at their slow, slow pace. Careful, if a male Megasaur gets his sap in your womb it'll take weeks for it to trickle back out through your vagina. Not a bad problem to have if you like that full feeling.

Mega Charizards X and Y: Despite being two very different pokemon, Zard X and Zard Y share most of their mating behaviors. They are very picky of who they have sex with, even among compatible pokemon. However, when they decide who they want to mate with, they usually don't concern themselves with consent. Here's the main difference between the two: Zard X is a top, and Zard Y a bottom. Power bottom, mostly. The dragon fire type makes Zard X a very volatile lover, able to cum and keep going like nothing happened, tho their stamina quickly runs out. Zard Y has a very thick genital slit, perfect on the female specimens, but it robs the male ones of a couple inches of cock, making them look smaller than they really are.

Mega Blastoise: Surprisingly shy, Megastoise is also picky with their partners, but what they look for in one is very different than other picky mons. Megastoise is very careful and considerate and wants to have a partner just like them. They are as romantic as feral creatures get and will groom and preen you afterwards. Be careful though, they cum like hoses and usually will turn your front side into a all white painting canvas, which they'll promptly lick off to clean you as an apology. Mating is the only time in their lives where they will actually hide their back cannons, not wanting to flood the room with their water discharges during orgasm.

Mega Alakazam: As most psychics, Megazam has small, puny genitals... but this is the smartest pokemon, and they can put that intelligence to good use. With their ability Trace they have a very high sense of empathy, and they learn of all your weaknesses in minutes. Give them some time, and they will find the most effective way to make you cum, even if they don't have to use their bodies for it. They usually handle spoons with their psychic powers, but they can replace them with sex toys!

Mega Gengar: This was a dangerous situation. Gengar is mischievous, but Mega Gengar is outright evil. They will hypnotize you, trap you with Shadow Tag and feed your brain nothing but wet dreams after you fall asleep, making you cum in your sleep and letting Mega Gengar feast on your dreams... and semen/pussy juice. They just love sucking you both ways, but they thankfully get bored fast and go away, letting you finish your dreams.

Mega Kangaskhan: As an all female species, the Khans (mother and junior) work as a team when mating. They will take turns riding your cock and face, which given the mother's size it's a bit of a risk. They have plump slits that get wet very fast, their instinct to mate being really strong, even for the juniors! Be sure to get them off fast, lest you want to be drowned in the mother's fluids.

Mega Pinsir: This mon is surprisingly tactful when it comes to mating. They'll grip you with their vice pincers... but, they will do so gently. They have weird shaped genitals: The males are like a string of bubbles with a swollen tip, the females have little pincers to grab onto you. They usually like to hover above the ground when mating, giving them their aerial control in this situation.

Mega Gyarados: A little awkward to mate with due to shape and size, but very rewarding. Megados likes to move, a lot. They will flail with their tails up and down and ram themselves full or ram you full with every thrust. They have low output among water types, but their lubrication is unmatched and can glide in and out with the slightest of efforts. Very recommended if you have the will to figure out a safe position to be in.

Mega Aerodactyl: Megadactyl takes mating very seriously and will always find a way to impregnate or get impregnated, a leftover instinct from the days they ruled the world. They don't waste time and love cervical penetration. Their sperm is very aggressive and swims fast. Thankfully, they are not compatible with humans, else we'd have little human-aerodactyl hybrids all over the world. It's a shame this pokemon went extinct, but with the miracle of modern technology, they are back and hornier than ever. 

Mega Mewtwo X: The Mewtwo megas are different enough to each get their section. Mewtwo X is like a sex coach, he will lead, direct you and show you all the ways to make them cum. As a legendary pokemon, they are hermaphrodites, capable of having sex both ways, but sadly sterile as a result. Mewtwo X isn't picky, but they are very demanding and will use their psychic powers to guide and control you. They are the ones in control, and they won't let you forget it. Be sure to bring hydration, these sessions can last hours and are very taxing.

Mega Mewtwo Y: Being one of the strongest psychic types means Mewtwo Y has overcome the problem that troubles every other psychic type: They have nice, thick genitals. Their cocks are slick and prehensile, while their slits are plump and grip tightly. As for their mating behavior, Mewtwo Y likes to explore. They like to try everything once, going from pegging, to bondage, to femdom (or rather, hermdom). They don't focus on a single thing, and like to eventually get to the logical end point of things.