Creating a similar effect to the "Zerg creep" found in SC

Has anybody thought of any good ways to go about creating something similar to the creep used for the zerg in SC?

For reference, it's basically a self-spreading ground cover that appears to be "on the ground" and can be interacted with by units (ie: the player.) It speeds up zerg units on it, for example.

The approach I've thought about using to create a similar modifiable terrain relative thing is trying to actually set tiles to what they would need to do, but I honestly have no idea how to approach something like this in Stencyl. I was hoping to be able to make something flow (like water) in a 2d environment without having to use actors like particles (repulsing each other and such)

Is it self spreading or does it spread as you add more building?

The creep spreads only with buildings, but I was thinking self spreading (with limits).

(Probabyl bad for performance)
Solution using actor as tiles for fragment of infected space. Self-spreading infecting 4 tiles around itself

[Start]
    1. Create Base actor (first building) - source of infection
    2.  Add infected tiles around base
    3. Adding infection tiles add its coordinates to the list
   
[Infection step]
    4. For each coordisnate in the list check 4 tiles around it to see if there are not infected tiles.
    5. If there is not-infected tile around current coordinate create infected tile actor.
    6. After checking set of coordinate rmeove it form the list


0- not infect
1 - base
2 - infected

Start:

0 0 0 0 0 0
0 0 0 0 0 0
0 0 1 0 0 0
0 0 0 0 0 0

Add infected tilesa around base

0 1 2 3 4 5
-------------
0 0 0 0 0 0  |0
0 0 2 0 0 0  |1
0 2 1 2 0 0  |2
0 0 2 0 0 0  | 3

Edge List : (2,1); (1,2); (3,2); (2,3) //List contains tiles on the edge of infeciton

[Infection step]
3 - newly infected tiles


0 1 2 3 4 5
-------------
0 0 3 0 0 0  |0
0 3 2 3 0 0  |1
3 2 1 2 3 0  |2
0 3 2 3 0 0  | 3

Create New Edge list = empty list

For coordinate #0 in Edge list
Check if 1,1 infected - no then create infected tile at position and add coordinates to New Edge list
Check if 2,0 infected - no then create infected tile at position and add coordinates to New Edge list
Check if 3,1 infected - no then create infected tile at position and add coordinates to New Edge list
Check if 2,2 infected - yes do nothing

Repeat for all elements in Edge list:
Edge list = New edge list

Edge list after first infection step: (1,1); (2;0);(3,1); (0,2); (4,2); (1,3); (4,3)

For enchanced effect change animation of tiles based tiles in neighbour hood.

PS. If you want it I can do it for my blog. The question is if your question was out of pure curiosity or do you actually need it.

I was originally wanting to use it, but for my purposes right now self repulsing actors will work. Ideally I would want one that you could interact with, but just curious at this point.

Thanks for the input!

In case you were curious....

http://t4upl.blogspot.com/2015/07/stencylzerg-terrain-infection.html