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For me, since I am in silver rank and I don't have enough cards to add up to my permanent power,
I always rent cards to gain the two daily chests rewards.

But if you don't aim the multiple daily chests rewards, then I recommend to get power at the end season.

But take note, renting cost is high at the end season.

Ye i wanna get the 2-3 daily quests everyday but renting power is pretty expensive. I only have 250 DEC and i need to use around 100 to get 40k power evreryday.