I started this game on September 3rd and honestly didn't expect i would be so interested in this game or try to climb by renting cause before the economy changes it wasn't really worthwhile to rent.
But after the changes it's far more viable to rent cards proceeded that you win matches but for up to bronze 1 you can basically just make do with 2 elements and renting some cards to use ideally common lvl3's along with a lvl2 summoner.
Now the tricky part is usually the lvl2 summoners to make the most of your lvl3 commons as it seems the rental market is sorely lacking in them but is saturated with lvl1 summoners which is weird, cause lets face it besides the summoners you can't use for free who would rent a lvl1 zintar or etc. 😕.
Now for bronze 2 you typically don't need to rent any GF(gold foil) cards as renting commons for 2 elements should net you enough Collection Power to make it all the way to bronze 2 as for bronze 1 that's when you suffer the choice of should you rent common GF cards or Rare and above.
My choice would be the Rare GF cards if possible that you can get for cheap rentals because it becomes far easier to keep track of your rentals compared to if you rent a bunch of GF common cards which you could of easily gotten for way cheaper as just common cards.
The real struggle becomes after you try to rent from Bronze 1 to Silver 3, there it's a fight for cheap rentals and constant refreshing but after a bit of persistence you can and will be able to snag a epic GF card for a decent rental price.
I would say the cheapest so far I've calculated i could probably rent enough power for Silver 3 for 30 days is about 1800dec give or take, cause I don't know how many renters will snub me on the final day of the season so you'll need to give it some leeway there.
I would highly advise to make a spreadsheet listing all the prices and collection power and price range which you could expect to rent the cards you want for cause it's not easy trying to remember over 20+ card prices
Now that I'm in Silver 3 how is it?
It's rough if you've only rented enough cards for 2 elements you really need a 3rd element or more to make it cause with the constantly changing rulesets and sometimes limitations on which element or what attacks you can use 2 elements just aren't enough and people tend to have legendary cards so it's an uphill battle from there.
Do you need to rent legendary summoners to help you in Silver 3 I would say you don't cause I have beaten people that used legendary cards/summoners, I would say the main key point to winning is understanding the ruleset properly and having the right cards in place. And Always Always make sure to glimpse through their battle history cause sometimes there are clues on what might come out and enable you to counter play.