Got my first 7* yesterday, was hoping for Dragon Man but I ended up with Mantis. Not the worst outcome, I guess. I did some dmg testing on rol WS; here's the rundown:
First, I ran some tests to find her ideal stat focus pick. Sp2 with 20 charges in each test case.
1.
Block Prof Stat Focus: I chose this as an indicator of her base sp2 dmg. I got 62033 + 93071 = 155,104 dmg total.
2.
Crit Dmg Stat Focus: I thought this would be the best for her at first glance, but the results were very underwhelming. I got 62725 + 94109 = 156,834. A total increase of 1730 dmg.
3.
Special Attack Stat Focus: I found this to be the best one for her. I got 66995 + 100517 = 167,512. A total increase of 12408 dmg. Decent.
These were the only ones I tested, as the other stats don't really affect her offensive potential.
Next, I matched her up against my 6* r3 sig 113 Elsa and 6* r4 sig 43 Herc in a WS takedown race. [Note: the sig levels don't really matter as they don't affect this fight]
Here are the final times:
[I did my best to finish the fights as fast as possible while using their optimal rotations]



Herc won, I am shell-shocked. Who could've guessed that, amirite folks? His final time was 1min 34secs. Elsa edges out the 6* r4+ equilavent Mantis with a time of 1min 51secs. Mantis narrowly misses out with a time of 1min 54secs.
My mastery setup is borderline abhorrent, so I won't post it for the eye user's sake. I don't run cides and I don't think other masteries make as much of a difference.
Elsa stays winnin'. I hope they make Mantis' furies last after her sp2 (sorta like hulking) because IMO she is very one dimensional rn and solely reliant on her sp2. Her tranquillize ability is cool and unique, but it's pretty difficult to incorporate offensively. I've managed to use it to block scorpion's sp1 without getting any poisons on me and counter void, which is great, but that's all there is to it.
She has cleanse on her sp1, but it is very situational and the only thing I see it being used for is to cleanse double edge and liquid courage. Her heavy also has some quirks. She will consume all her mixed emotion passives upon charging heavy, no matter the length of time you hold it for. So essentially, a node or a champ that requires them to be knocked down will effectively disrupt her ramp up.
She's great if one sp2 KOs the opponent, but if it doesn't, she needs to ramp up all over again. The sp3 tranquillize seems useful on paper, but usually if you need to use tranquillize (debuff counter) for a fight, you need it from the get-go. A sp3 is a long way ahead. Chances are, she won't even make till then.
She is getting a tune up, and I do think she needs it. Whether this tune up actually delivers, we'll just have to wait and see...