Primarily, it can be controlled to keep opponents at an ideal distance or stretched in order to make Monferno appear larger
Armarouge can use its ability as much as it wants in a turn, which synergizes with Ethan's Ho-oh ex because that card can attach two fire energy from hand onto it, and Armarouge can move that energy to the active Pokmon so it can attack
This is one of the few that give it an environment to thrive in
A key part of its history is the associated "Ancient Mew" promotional trading card, distributed to audiences during its theatrical run
For example, imagine your opponent has a Mew VMAX: Zacian VSTAR with Choice Band can easily get rid of it even with Oricorio on the field and even 1HKO a Duraludon VMAX
You could access one of the activations in a monocolor deck, but access to both activations required a two-color deck