How to create a blood wall drip effect?

Hi guys,
I'm currently working on my first game. I'm about 2 weeks in and I've already learned a lot, however I'm having trouble right now. I'm trying to create a blood splatter effect where whenever i shoot an enemy it spurts out blood particles, then when those particle collide with the floor or walls, i destroy the particle and pull from a pool of decals which i then spawn at the point of collision (I'm using EasyDecals to project the decal onto the object). This works great, however, i want for blood that lands on a wall to drip down, but i also want it to leave a trial behind when it drips. The video below at 0:17 seconds in displays the effect i want to achieve:

My game also uses pixel art assets so i thought that i could pull from this video above. Could anyone help me out with this? I don't know how they do this. At first i thought they put another decal onto the existing one with an animated texture or something like that. But now I'm not so sure. Maybe they used a mask to slowly "reveal" the hidden part of the decal, giving that drip effect, by the drips move at different speeds so I'm not sure about that one either. Maybe they are not using a decal at all but instead "painting" the blood onto the wall's texture? I say this because of their showcase at 0:45 seconds into the video where the gibs seems to be "painting" across the surface. The only problem i see with this is that i am reusing the same texture for a lot of my walls so if i were to paint onto the texture of one wall, that new painted texture would also show on all the other walls that use that same texture. I was listening to John Carmack's Quake 2013 talk on the principles of light and he mentioned that he used something called a "mega texture" for RAGE. How plausible would something like that be to implement with my limited skills? Also how would a method like run performance wise? My game uses very basic shapes, mainly giant cubes for walls and floors, no round objects at all as I'm going for the very old school shooter look like Wolfenstein 3D.

If anyone could help me out with this i would be very grateful.