An excellent way to popularise "monstrous" champions would be a PVE MECHA event

The MECHA skinline is one of the only 3 major skinlines showcasing solely monstrous (I also include humanoid champions with especially unnatural appearances in this definition) champions, along with Guardian of the sands and World Breaker. Being the most popular one of the three, it is probably the best option we have to bring interest into monstrous champion, since most of them lack popularity and, because of it, are really often shunned at in terms of skin release.

In a marketing perspective, it's quite normal that they are often ignored by Riot in terms of skin release, since they'll sell a lot less than, well, almost literally every single female champion in the game and so on. But, the thing is, the very fact that monstrous champions gets ignored by most and even by Riot at most times contribute to their unpopularity, but if a major event would happen in the favor of our cast-away champions, it is sure to enhance their popularity by quite a bit.

The MECHA skinline is a PERFECT skinline for a PVE event in the likes of starguardian and odyssey, while being a skinline who's already a little popular but who (sadly) doesn't get much attention in terms of addition. New MECHA skins for other monstrous champions would already be formidable, but making a PVE gamemode featuring them is sure to bring a lot of players to try monstrous champions and bring interest. This would ultimately both cause monstrous champs to be less shunned at in terms of gameplay changes and in terms of skin releases, AND would also bring a PVE event in a kick-ass theme.