With people stuck at home, puzzles, parlor, card and tabletop games boom
The Starter Commander Decks are five, standalone Commander decks, designed to come in at a lower price point (somewhere in the neighborhood of $20-$30) than the other Commander products released alongside new sets
Since Rulik Mons adds green to your Goblin deck, you can start playing cards like Doubling Season and Parallel Lives to start doubling up on your token generation
(Mana abilities can't be targeted.)
Together, these cards form an infinite loop: you sacrifice Familiar to Seer, drain your opponent, then use Samwise Gamgee's Food token to bring Familiar back, repeating the process until the opponent is out of life
For the ability that it has, it makes sense