The most commonly used rune trap and arguably the most efficient is 2,1,2,Ex close rune. You can use it as is or you could end trance combos with 1,1,skydrop and then perform the rune trap immediately after that.
An example combo just to give you an idea is: jip, b3, 1+2, dash, 1,1,2, trance, jip (or meterbuild), 1,1, skydrop, [2,1,2,Ex close rune].
I'm not able to check the damage on that combo now but it does between 26-30% and then you add the rune trap for an additional 15%-45% depending on how many bars you want to use which as you can see potentially shaves off 70% and sometimes more of the opponents health bar .
You can end any trance combo with 1,1 skydrop linked to the rune trap. The variations are many so have fun