dragon, drag on, drag in

Dragon or dragon ( one word ) means the mythological beast, possibly fire-breathing--
He plays a computer game in which he is the knight who slays the dragon and rescues the fair maiden.
We all like to see the dragon during the Chinese New Year festival.

Drag on or drag on ( two words ) means to pull heavily or slowly; to draw along the ground or floor ( drag ) over or atop a space, place, or substance ( on ) --
We're supposed to carry the bride's train, so it doesn't drag on the floor.
We shouldn't let the flag drag on the ground.
Drag on may be used figuratively, to describe an event that passes slowly or tediously--
The meeting seemed to drag on for hours.
The afternoon seems to drag on when you watch the clock.

Drag in or drag in ( two words ) means to pull heavily or slowly; to draw along the ground or floor ( drag ) within a space, place, or substance ( in ) --
Don't let your coat drag in the mud!
Pick that up, so it doesn't drag in the puddle.
Drag in may be used figuratively, meaning to introduce irrelevant matter into a discussion--
He always has to drag in that proposition we voted down months ago.
Do you have to drag in that old argument every time we have something to discuss?

Now that you know that, you can say--
"The parade seemed to drag on while we waited for the dragon, moving slowly so that its tail wouldn't drag in the mud."

Note--not to be confused with "dragging", a participle of "drag", meaning to pull heavily or slowly along the floor or ground--
Tell him to stop that; he's dragging it in the mud.