So, in order to unlock the other figurines, you need to defeat the golden echoes (the cosplayers). To spawn a golden echo, you need to continuously defeat the enemies echoes in that room, which include dark purple (lesser echo), bright purple (normal echo) and blue (greater echo), until the golden echo spawns. Some rooms may not adhere to the colour-coding, and the different colours may actually be echoes of completely different cosplayers, but in general each room follows the rule of dark purple (weakest in room) -> bright purple (middle) -> blue (strongest normal) -> gold (strongest rare).
The combo number of defeated enemies in a room is on a singular room basis, so leaving the room will not reset your count for that individual room, but at the same time it will not count towards the other rooms. (i.e. if you defeat 30 echoes in a row in the first forest room, it will only total to 30 in that room, no others) However, if you are defeated, or the golden echo spawns in that room, the count for that room will be reset. The combo requirement for each room varies. Some of the early rooms only require a combo around 30-40 for the golden echo to spawn. For each of the two new rooms added for this version, I needed a combo of ~150 until the golden echo spawned, so it took around an hour of grinding.
When the golden echo shows up, there is a heartbeat noise that accompanies them. Once defeated, you'll get that cosplayer's figurine and that character's scenes from the old version of the game.
