The Pseudo-Dragon: From Edwina, the familiar of Jallarzi Sallivarian, to Afreeta from Quag Keep, to the captured Pseudo-dragon in U1, the Sinister Secret of Saltmarsh the idea of a small dragon familiar was rife in the early days of our hobby.
And why not? Who doesn't want a dragon familiar? Isn't the idea of owning a dragon a very cool one? Of course it is.
Like most memes, this one fell out of favor because soon, every Tom Strongblade, Dick Swiftwand, and Harry Sneakthrift was walking around with a dragon on their shoulder.
Historically having a pseudo-dragon familiar provided magic resistance and what it sees and hears within 24" including invisible objects.
The Deadly Touch: Recently one of my players died to yellow mold. He had never heard of yellow mold. (!)
The early game was filled with things that punished people for touching them. Green Slime. Yellow Mold. Rot Grubs. Each one with a specific way of dealing with them. You can see it from the green slime card in the board game Dungeon (tm) or the frequency with which refuse piles are filled with rot grubs.
That was really where part of the wonder of the early game came from. In the next room, what would you find? Would you die at its touch, or would it be a fabulous chest filled with jewels and wealth?
The violent and sudden nature of the deaths caused this trope to fall by the wayside, but you can see a resurgence in these types of encounters in modern games.