idealy you'd want a mono deck for level 3 grinding, heres what i would use, feel free to use what you want, just examples. 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f0 5f2 5f2 5f6 5f6 5f9 5fa 5fa 5fa 5fa 5fa 5fa 5fc 5fc 5fc 5fc 5
there are much better fire decks if you look threw the forums, wanted to make it simple though.
5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rg 5rk 5rk 5rl 5rl 5rl 5rl 5rl 5rl 5rm 5rm 5rm 5rm 5rm 5rm
harder to make one for time, so i'll just suggest this.
keep in mind there are better decks, these are just examples.