Well, if you've marked a double on your side, and your opponent hasn't, then who's the fool. Therefore, the strategy for marking here differs from the standard one – you need to either go for a double vs. double or ensure that no one has a double.

Red can't avoid the opponent having a double here if they want to get one. If Red's first mark is Necropolis because it can't be given away, then only two marks remain to remove four of Blue's castles – Dungeon, Castle, Tower, and Inferno. On the other hand, Blue can easily mark three of Red's castles. As a result, Red is left with either a flux for a double Inferno or a double Inferno against a double Dungeon/Castle – according to my calculations, this is the best he can achieve if Blue goes for a guaranteed double. In my opinion, neither option is very good for Red.

Marking on this map is certainly a very interesting topic. I think the most optimal option for Red in any situation is to remove Necropolis, Dungeon, and Castle. Blue can then, at his discretion, either remove Swamp, Rampart, and Stronghold, or take one of these castles for himself and mark Inferno instead, so that it doesn't go to the opponent either. In this case, having the last word in the castle marking phase, Red can choose not to remove Dungeon or Castle for Blue – then Blue will have to choose between a double vs. double or a non-double vs. non-double. I would call this strategy for Blue a non-guaranteed double, in contrast to the previous one. Of course, I may be wrong about everything I've said, and this is just my opinion. And again, all these arguments are based on the assumption, taken as an axiom, that a double is an absolute overpowered advantage, just like Necropolis. But this can be doubted.

Added 25 minutes ago
I thought about it some more... The question is, is it beneficial for Blue to go for a non-guaranteed double, because in this case, for the opportunity to upgrade Ducks by taking Swamp, he gives Red the opportunity to upgrade Angels and get a Stable if he chooses Castle, or a double Mana and Portal if he chooses Dungeon. What Red should choose in this case is also not entirely obvious.

Added 11 minutes ago
Damn it, I want to sign up, but the lack of time for all the Tournaments and the complete uncertainty about the rules don't allow me to do so.