I went outside and gathered some moss, a chestnut, half a snail shell and some other random bits for the base.
I used a hairdryer to dry the pieces I found outside.
I glued on gras tufts into several recesses on his body.
Here i got a bit ahead of myself and started basecoating the metal areas. In retrospect it would be better to do that after airbrushing.
Aairbrush brown and green
I airbrushed some brown to cover all of the base, then proceeded to paint all the grass tufts and other plant materials on his body. The rest of the model I tinted with a light green, like a light source above him. Several areas were still the base primer, but I knew the weathering I would apply would cover them.
Chipping medium, armor paint, rust texture and banner
In this step I mixed a bright pink with chipping medium and applied a pattern to the armor. I also went ahead and applied rust texture in most recesess and painted streak marks of rust running down in some areas.
For the banner I simply used some kitchen paper towel and dampened it with PVA glue and water. then I wrapped it around his weapon and dried it with a hair dryer.
Chipping, washes and more rust and dirt
Now i used a stiff brush and water to activate the chipping medium and wear down the paint on his armor. When this was done I painted some more rust streaks. I also used some brown paint and a toothpick to flick dirt splashes on the lower part of the model. The banner was painted in the same color as his armor and then dirt was splashed onto it as well. The paper towel absorbs the thinned paint giving a effect just like dirty cloth.
I made sure I painted the tips of all the spikes on his back black and used gloss varnish to give them a pointy shine. I also applied gloss varnish where his base was not glossy yet, for that wet mud look. I applied black or brown washes in areas where there was not much paint yet. I also flicked some more brown splashes onto lower parts to get the effect of him running trough mud all day.