Blink it, or reanimate it, play it with other artifacts, or with Sphinxes that pillow fort players, and suddenly the person who just gained 100 life with an Ajani ultimate, or even went infinite with lifegain may find themselves one turn away from losing the game
Arthur is an incredibly powerful card that allows you to earn lore with your weak questers like Lilo, Making a Wish and Pinnochio, Star Attraction, then bounce them back to your hand to keep them safe from challenges - while also rewarding you with two lore for doing it
Blue Every Final Fantasy game is full of mages weaving complex spells and summoning forces of nature to save the party
As such, we got a lot of precons
The low cost makes it easy to hold up alongside other interactions
Most of the time, Cumulative Upkeep costs are some amount of mana, though some cards (and this is especially prevalent during Coldsnap) would ask for some other payment such as paying life or sacrificing a creature