An Axolotl inspired this pokemon. It has no arms.
Wooper
This is the only mega pokemon to lose a type when it mega evolves.
Mega Aggron
Not margarine + Something that costs nothing?
Butterfree
Ho-oh created this legendary trio.
The legendary dogs/beasts.
This pokemon is a mythological counterpart of a Tapir called a "Baku." This is also the origin of its dream based abilities.
Drowzee
These two pokemon gained +70 in one of their base stats upon mega evolving.
Mega Beedrill and Mega Slowbro
Revolvers have 6 of these + What you plant to grow a tree.
Bullet Seed
This single legendary has 3 different forms
Mewtwo

Dragalge
This mega pokemon did not receive a +100 BST until gen 7 when it was buffed.
Mega Alakazam
Type of precipitation + What a moonwalk is
Rain Dance
None of the pokemon in this trio have ever been in OU.
The Titans/Regis

Sandshrew
This mega pokemon learns no STAB moves for its new mega type.
Mega Pinsir
A 1500 year old board game + slip, hitch, noose, overhand and figure 8.
Chesnaught
This generation where weather is the most integral to the meta ironically included this pokemon trio.
The forces of nature.
This pokemon is based on a real sea creature known for shooting with its larger claw.
Clauncher
These two pokemon can take on the form of a mega pokemon despite not owning a mega evolution.
Mew and Ditto
The time between sunset and sunrise + There are 7 of these in a week.
Night Daze
One of the pokemon from this trio represent emotion.
The Lake Guardians.