Cant light a tar patch I'm afraid.
If you want a patch you can light, get trick arrow secondary. The power oil slick from trick arrow can be lit 
Also, for lighting ninjas is just good enough. Your lvl 26 pet has fire attacks including a few aoes that will light it.
- @DSorrow - alts on Union and Freedom mostly -
Currently playing as Castigation on Freedom
My Katana/Inv Guide
Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. -Einstein
Just be aware, Oil Slick is bugged so not everything lites it up 
How do I light a tar patch? Is it possible? I have ninja/dark lv2 mastermind, so I could swap the primary if needed.