He is way better than a Merfolk Sovereign in the Merfolk deck
Raul, Trouble Shooter is a nice synergy piece as long as youre on the self-mill train, and doesn't require the hoops of a card like Conduit of Worlds to cast things out of the graveyard #25
(It can deal excess combat damage to the player or planeswalker its attacking.) Its insatiable hunger quickly depletes a region of prey
You can even take this a huge leap further and build a whole deck around Fog, like my friend Lenny did with his Atraxa, Praetors Voice Turbofog deck
[one_fourth stack="responsive"] [/one_fourth] [one_fourth stack="responsive"] [/one_fourth] [one_fourth stack="responsive"] [/one_fourth] [one_fourth_last stack="responsive"] [/one_fourth_last] Leonin Warleader is pure value
By the way, Im kind of assuming that this is going to be read ahead to the final chapter, and thats probably true 90% of the time