Cactus. One of the few 6* I have, but on Nutaku.

Stats:
HP: How can I say that... even 5* have more HP than her. Even the thiniestglass has more HP.
ATK: Just like HP. Her ATK stat is depper than Lotus Lake abysses.
DEF: That's a good stat, but with her bad HP it's not useful.

Skill
x5 damages to one enemy with 46% skill act.
x5 damages with 46% skill act.
46% skill act. I'm pretty sure it's the best skill chance of every girls in the game. Just add a little x1.2 skill act girl and she is over 50% skill activation chances.
With x5 damages on one enemy, that's very good.

Abilities
Increases Shine Crystal drop rates for all by 30%.
Just no. Even worse than Cattleya Solar Gauge ability. BUT, that bad ability is usefull for the incomming stuff.

+20% ATK for all
Not the higest buff in the game but it's decent at least. Not good, not bad. It can help the other girls but with her low ATK, it's not that good on herself. But it helps anyway since she will be an hyper offensive girl.

Crit Rate +15% & Crit Damages +40%
The Crit Rate buff is good but not that good but Crit Damage buff is really nice. But she may need other Crit allies to be a solid Crit girl. I mean, she is very solid but with some Crit Chance buf support.

60% chance to Act Again.
Re-act girls are so underestimated. It's a rare and broken ability, espacially on girls like Cactus. 60% is the best chance of react in the game (just behind the 100% but turn 1 only). And THAT'S her hidden trump card.
Without it, she is just a good offensive 6* with high skill chance. With this ability, she is like TWO good offensive 6* with high skill chance, 60% of the time.
Now, use her with the right allies (with Crit,skill act and damages buff) and she will be a monster.
Even a 5* with re-act can be very good if she re-act. A 6* like Cactus with all her assets is just OP.


Conclusion
Despite her poor stats (espacially ATK) and that bad Crystal Drop ability, she has an awesome skill+skill act and a good set of abilities.
Like I said earlier, Crystal Drop help her a lot. Not by itself but it's bad enough to allow her a lo of other abilities to balance it. I'm sure if she had something better, she would not have Crit or the Re-act. And she would be... just good.
That Re-act just make all for her. She can do her job twice ahd she do it well. Her recent Skill damage boost make her even better.
If she is used in the right team, she can be one of the best offensive girls I guess.
I already said that but re-act is a strong underestimated game style. It's a high risk, high reward style due to the RNG and the lack of re-act chance buff but if the re-act occurs, it can totally change a battle.

Final verdict:
A glass canon made of pure glass and pure canon. She could deserve a S-tier for her ridiculous power but I will only give her a solid A Tier. In my opinion, she lacks a little something to be S Tier. A tiny tiny not important thing like... HP drain. For me, the S Tier hare the girls able to survive the hardest battles and carry all the hopes of her dead friends by herselves. Even with that incredible power, Cactus can't do that. If she had just x4 damages and HP drain, she may be able to win against the Death and kick her ass with ORAORAORAORA power.