I’ve probably mentioned this before, but the Rahi archetype from BCOR is in a bit of a weird spot design-wise, since I never really got it into a state I’m totally happy with. It’s therefore pretty high on the list of things that might need an overhaul in the future. But until that happens, they’re pretty much a hodgepodge of not entirely thought-out themes and mechanics, and right now I’d like to point out something interesting that emerged from that without much planning on my part.
Bog Snake, Rahi 
Mahi, Goat Rahi Ruki, Fish Rahi
Pictured above are examples of the three most commonplace variations Rahi come in: Level 4 Pendulum Monsters who can Special Summon themselves from the Pendulum Zone and give effects when used as Synchro Material, Level 3 Pendulum Monsters with effects that trigger when going to the GY or getting banished, and Level 2 Tuners with handtrap effects that require banishing themselves plus a Rahi in the GY. The bottom line here is: Their gameplan involves them appearing in and moving between just about every location the game has (except non-Pendulum S/T Zones).
Why do I feel the need to highlight this? Because, if you think about it, it matches up perfectly with the way all the various non-civilized creatures known as “Rahi” inhabit every nook and cranny of the Matoran Universe. So I’m seriously considering keeping it around as a central point when the eventual redesign happens, even though Pendulum Monsters and GY effects in particular sounds like a somewhat moronic combination. With a bit of streamlining and proper balance considerations, I imagine this gimmick could be a lot of fun.