Other cards you could add are Thassa's Oracle, Bident of Thassa, Retreat to Coralhelm, maybe High Tide, Tidal Influence, Tidal Surge, Tidal Wave, or high-toughness Crabs like Ancient Crab to hold the fort while you mill
Karumonix, the Rat King, and Lord Skitter, Sewer King are two Rat lords which help you swarm over every inch of the battlefield, and the classic Marrow-Gnawer has long since been a champion of Relentless Rats decks everywhere
* The filler with the most sources is the Discard Filler V1 Card with at least 27 , followed by the Black Border Filler Card with at least 24 and third one being the Black Border with Barcode Filler Card with 17
Every version of this MTG card has seen a price spike, and while the basic version saw the highest jump, others are close