A tiny example from when I was replaying the second chapter of Tales of Monkey Island. During the sword fight with Morgan, thereís a dialogue option to try insult sword fighting on her ("Every enemy Iíve met, Iíve annihilated!") which she immediately counters ("With your breath, Iím sure they all suffocated!"). Clever, but I wondered why they used an insult from Curse, when insult sword fighting is more iconic of Secret. It finally hit me: itís because they were fighting at sea, and Curse established that you have to use rhyming insults when fighting at sea. Welldone, Telltale. — Objectioning
Further to this, the compliments/insults Guybrush uses at the Crossroads when duelling the swordsman and trying to bolster Morgan are the insults for fighting on land.
The spell that LeChuck casts on Guybrush in the fifth part in Curse is the same spell that LeChuck casts on him at the end of MI2. The first time it brainwashed him completely, but the second time it only left Guybrush with a foggy head and childlike behavior, because he had built up a resistance to it, which explains how he managed to escape from it the first time.
Wally B. Feed's nickname is Bloodnose the Pirate. Bloodnose is Wally's middle name.
Lemonhead thinks that the midway games in the Big Whoop Carnival are rigged. He may be right, considering that Dinghy Dogô's scale always shows 98 pounds, no matter how many items Guybrush is carrying.
How did Walt the dog appear in the tunnels under Dinky Island to steal LeChuck's arm? Because they are connected to the tunnels under the Phatt Island waterfall.
The Monkey Island series has many, especially in the first game The Secret Of Monkey Island: When you take into account what Stan says about the monkeys having driven the ship back to Melee Island, combine it with the fact that you can teach monkeys to do things later in the game, and the general laziness of most of the characters, it comes down to this - Herman Toothrot and his companion taught the monkeys to drive the ship so they could relax, but the monkeys drove off without them, leaving them stranded on the island. This led to Herman's partner killing himself, and Herman going insane from isolation.
In the same game there is the extremely creepy section with the shrunken head and the labyrinth made out of body parts and mushrooms. The mushrooms were probably growing on the rotting bodies. If you don't have the shrunken head to lead you, this will be an endless maze of different rooms. An endless maze of body parts surrounded by lava, people who have probably been killed trying to do the same thing as you. Why does the shrunken head know the catacombs so well? Could he be from there, ie, could all the body parts still be alive? It should be noted this section is completely uncharacteristic of the rest of the game.
It must be said the reason the shrunken head is so good at navigating you through the tunnels is because it belonged to an expert/world's greatest navigator who then died/got killed and got his head shrunk to be used as a tool.
Earlier in the game you come across a stump in a forest. In an early version of the game Guybrush will be able to enter it (although you don't see what's inside it) and he'll say that there are a series of catacombs. Consider that later in the game you can enter a series of catacombs (the labyrinth mentioned in the previous example) and it makes you wonder whether it goes on indefinitely underground. The forest itself can often be a maze which is foreshadowing it, especially if they are actually connected.
In the third game, however, there is an easter egg where you find a hole inside the Goodsoup tomb that leads to the stump, so perhaps the stump is just some kind of temporal portal or something like that instead.
Just like all the other skeleton pirates Guybrush shot out of the water. They are all stuck on the seafloor, unable to die. They can't even rebuild themselves because their limbs are floating all the way up on the surface. Murray was lucky to reach the shore.
Why do LeChuck's unfortunate victims want to serve him, especially after he kills them? Because if they don't, he might do something even more horrible to them...
Why are Sharp Tooth and Red Skull no longer part of the cannibal tribe? Because Lemonhead sacrificed them to the volcano god.