Sacrifice to Mathlann gives you instant black ark on the sea AND resting black ark in your hiring pool.

check screen shot. you can get 2 black arks every time you do Sacrifice to Mathlann.

this is even worse case for AI because AI player upkeep for black ark is free and they have usually broken AI on black arks, so this causes massive turn lag becuase broken AI black arks is stuck at some point.(check last screen shot)

check this link too : https://new.reddit.com/r/totalwar/comments/1cw7f3o/lmaoo_wtf/