A permanently purchased item in the game becomes less valuable over time.
"Seasonal items, even ones you spent money on, will most likely come back at some point. The only thing making them valueable is scarcity until they return, and until then are just used for bragging."
"Every single item from crafting to farming becomes more expensive/worth less. Waiting to spin for a chance to collect the cats takes exponentially longer, capping at 12 hours."
"characters in the game are never completely useless its just that some of the stages are getting harder over time."
"To be fair it's to soon to say but judging on the cards we see appear in the season passes since release it sure seems like the game has power creep (which most similar games do)."
"Early game items or items that you can obtain without paying are vastly less powerful than anything purchased or would require so much grinding that you’d have to make it a job."
"When this game released, you could only have characters up to 5 stars (the best characters available). After some time, they released 6 star characters, then S-class characters, then mythic characters, and then limit break for mythic characters. It is important to note that mythic characters made almost all other types of characters obsolete."
"They sell "limited" items which are basically a gamble. They can lose or gain value in the shop."