use an 'execute' (repeating) command block to check for players within a certain radius/ area. If a player is detected, the command block should trigger a redstone block to be placed.
an 'impulse' command block (containing your dialogue) should exist next to where the redstone block is being placed.
This way, the impulse command block is only triggered once, as, after being triggered, it now has a redstone block permanently placed next to it.
Personally, my favorite to work on was "Ultra Trident Jumper". It used the trident riptide command to give a new spin on the tried and true Minecraft parkour format.
My favorite adventure map that I have played (recently) was "Lost in the Garden" (Lost in the Garden Minecraft Map (planetminecraft.com)): it has some really interesting non-euclidean geometry, and interesting puzzles.
I have been using the following command for things like this in my own maps /execute as @a at @s if block ~ ~-1 ~ minecraft:BLOCKNAME run kill @s use this for an always active repeating command block. where '@s' means 'current entity'. the 'at @s' bit ensures that the command is being run at the location of the entity in question, rather than from the command block itself.
I don't think that MCedit works for version 1.14.4 unfortunately. However, I would suggest downloading the datapack "blingEdit", which is like MCedit, but you can use it in the game.
