Pokemon GO's September update brought in the legendary Pokemon Entei, as well as a whole set of new research tasks that players can complete to unlock new Pokemon encounters - including additional Shiny Pokemon.
As well as a new variation of the Pokemon Spinda, players can find Fire-type Pokemon by completing tasks this month (and completing seven days' worth of tasks will net you the opportunity to catch Entei).
One of the most interesting additions this month comes in the form of Growlithe - the first Generation fire type Pokemon.
The little dog has now been given a Shiny variant - which can lead to you getting a Shiny Arcanine! - so it's worth keeping an eye out for the quest that triggers its appearance.
How to catch Shiny Growlithe
There are a variety of ways of catching a Shiny Growlithe.
Currently, your best bet is to spin different Pokestops until you receive the 'Use 10 Berries to catch Pokemon' challenge.
Then, you need to complete the challenge and encounter the Growlithe (it has much higher odds of being a Shiny when encountered from the challenge). It'll have between 440-476 CP, and usually has good stats.
You can also encounter the Pokemon in the wild - though odds of a Shiny encounter via this method rest at about 1/450.
Shiny Growlithe - How good is it?
Once you get yourself a Shiny Growlithe, you can evolve it into a Shiny Arcanine by feeding it 50 candy.
Once evolved, you'll have an Arcanine - which is a useful Fire-type Pokemon.
According to Pokemon GO Hub:
Pokemon GO Arcanine is a Fire-type Pokemon with a max CP of 2839, 227 attack, 166 defense and 180 stamina in Pokemon GO. It was originally found in the Kanto region (Gen 1). Arcanine is vulnerable to Ground, Rock and Water type moves.
Arcanine best moveset is Fire Fang and Fire Blast, with a cycle DPS of 21.55 damage per second.
In truth, Arcanine is a good fire type to have as a backup, but it's by far in a way not the best fire type in the game by a long shot.
Pokemon GO - September Research Tasks:
Battle Field Missions
Catch Field Missions
Raid Field Missions