Popping in here, because this topic specifically has always interested me.
It's been discussed before, because we don't really 'own' the game persay. It is KovuLKD's game, and advertising is an iffy topic when it comes to that. However, I have actually in the past, on a discord server of mine, hosted an advertising campaign that didn't really do too well, mainly because not many were interested in advertising the game through the discord server.
I believe holding possible contests, or events, throughout dA, the forums, and other means, can surely help boost advertising to other people unbeknownst to Feral Heart. Contests such as FH Trailers, where creators from the community can make trailers for the game. Feral Heart has a dA group, which can be used to easily host contests to advertise the game in order to bring in more players.
Advertising is difficult, 100%. Advertising has a direct flow, it's catered to people who are interested in the target topic. Feral Heart, being that the game is very outdated, and lacks the same sustenance as other games may have, will not please or satisfy many potential players. However, I'm sure there could be something in place that could help advertise the game.
Perhaps with more updates and patches, during the same interval there can be trailers put out as a contest in the same span that a new patch is put out, in order to showcase the new updates as they come. This would surely be helpful to new players coming in, and people who may be interested in the game, but are iffy on climbing aboard.