Considering rerolling takes so long, and you need a new email every time (or salt your current one), we don’t really recommend going for more than 1 5-star character if you want to reroll.
I’m not going to recommend the rate-up banner because that depends on whom the current unit is. For example, at release is worth going for Suomi, but you might be reading this after her banner is gone. Check our tier list to see if the rate up is a good one.
Assuming your email it’s hello@gmail.com:
You can use on most games hello+1@gmail.com, hello+2@gmail.com, hello+3, etc. as “new emails” in the database for the game, but Google will consider it your email, and you will receive in your normal inbox.
If that doesn’t work, you can also start adding dots to your email, using something like h.ello@gmail.com, he.llo@gmail.com, etc. and it will work the same way (but more limited, since you can’t add infinite dots compared to using +999).
That is called salting and works in 99% of gacha games, since databases will count them as a new account.
If the current rate-up banners are not good, there is only two options I will always recommend rerolling for; Tololo and Qiongjiu.
They’re amazing even nowadays in the CN version thanks to the expansion keys.
You get for free Sabrina, Peritya and Vepley, so I would avoid rerolling for any of those 3 girls.
The core of fire teams with the most insane single target damage in the game even though she's a standard doll. She can do some decent AoE with her skill 2 + fixed key 4, but I don't recommend using it as the skill is very awkward.
Her movement range is also quite low so don't bring her in big extraction maps. Her ultimate stacks can go down very fast and hard to maintain so you need to micro manage a lot to get max damage with her team.
Worth going for high dupes as the higher you go the crazier she gets, but definitely not necessary (v3 is good enough imo).
V3 is the breakpoint you want, after that is just how much more damage you want her to do because from v3 to v6 her damage will keep going up.
This key not only boosts her damage but also allows her to use the fire boost set and utilize the burn damage buffs from Vector and Centaureissi's expansion keys. A very nice key to get for fire teams.
Great early game DPS option, good burst damage, extra action is broken but quite limited due to long cooldown. She gets better with dupe and being a standard pool unit it's quite common to get spook by her so maxing her is only a matter of time.
Low movement range without extra action. This changes entirely when her new key comes out, becoming borderline broken getting the extra action every turn.
But that also depends on if you have other water units on the field and the amount of dupes you have. Becomes top tier later on so you won't feel bad about getting her dupes, also boost other water unit value (sabrina, zhaohui, colphne).
V5 is the breakpoint to get max damage out your Tololo, she will get better and better starting from V2
Effectively a 100% damage boost as now she can get her extra turn every turn when any ally deals hydro damage and if you have Springfield's V1, you can give her 3 actions in a single turn.
A crazy good key and a must have if you want to use her effectively.