I really do wonder who was attacking Mariejois. It feels too early for Dragon to make his move on it, and Blackbeard has Pluton and Poseidon to find.
But who else but them would do it?
It's some combination of the Yami/Catarina touching Saturn letting Teach use the Abyss. People are assuming the Abyss is an Imu-only thing, but, we already have evidence it exists outside Imu:
Nami's explanation about Demon Summoning makes it very likely that other people besides Imu can use the Abyss to summon things/people.
While I think Catarina will turn into Saturn, after touching him in Marijoa, it's entirely possible the Yami lets Teach connect to the Abyss naturally. Imu's "Seals" are all based around ocean depth, whereas Teach's Darkness crushes people like the pressure of the deep sea, and has an attack called "Dark Water."
Laffitte has already been to Marijoa, when he interrupted the meeting between the Warlords Doflamingo, Mihawk, and Kuma, and the Marines Tsuru and Sengoku, and Laffitte was seen near the Redline recently watching the Gondolas get sabotaged by the Revs. Laffitte has already snuck into Marijoa, Laffitte can easily do so again to create a Magical Circle for the Blackbeard Pirates to use. In order to use the Abyss, you do need the Mark; I'm thinking Teach's Awakened Powers will come in play here, since we haven't seen them, yet. Teach will give his crew Marks of the Abyss.
Blackbeard: "Zehahahah! Well, stop enjoying the show... and get to prepping!"
Yeah, it's the Blackbeard Pirates invading Marijoa.
Teach using the Abyss to fuck over Imu really fits his character. Teach also has no problem splitting up his crew. Only half of them took on the Heart Pirates, and only Kuzan and Auger went to Whole Cake. Kuzan went alone to Punk Hazard.
We also know the Abyss is an instant teleport from Sommers, so Teach can get in and out quickly, no matter where he goes, if he's using it:
Sommers was in the middle of a conversation with someone in Marijoa, when he was teleported in his undies to Elbaph. That's how fucking fast the Abyss is, he didn't even realize he had left the Holy Land. It's instantaneous transport, like Goku's Instant Transmission from DBZ.
Teach gaining this power would let him raid wherever he can set Magic Circles up. Egghead, Elbaph, Wano, Fish-Man Island, Marijoa. Literally wherever he wants, and he has an Invisible Guy, a chick who can turn into anyone else, a former Admiral who can use Ice to go wherever, and two fliers in Stronger and Laffitte, on top of a dude who teleports.
Blackbeard is about to pop off/pop up all over the place.