Many token creators create a single creature token when their abilities are triggered, but Namor can create tons of merfolk tokens based on the number of blue mana symbols used in casting your noncreature spells
We'd already observed that the scary Solgaleo/Skarmory decks that everyone has been worrying about are nowhere near the top of tournament leaderboards, but now it's clear exactly where things lie, with Giratina decks colonizing the top of tournament tables for a complete fortnight
During the End Phase of this turn, Set all monsters affected by this card's effect
The second reason I think it makes Magic better is that it disrupts the expected flow of the game, it mixes it up and allows situations where turn two things are happening on turn one
If you want to combo win, then you can get infinite mana with Displacer Kitten and Lotus Petal, or you can grind out value by recasting cards like Dross Skullbomb to draw cards turn after turn