I know this is mostly bug reporting boards, but I need riot to see this cause they are releasing item madness called "Umbral Glaive" on PBE, and next patch on live most probably.
I'm just a regular support player who wants to play Senna (so yeah it's maybe a selfish of me to write this post, but Senna will be 55% win rate and up to 95% ban rate next patch probably if she doesn't recieve any nerfs.)
Not only do people keep learning her, but she is already one of the best supports, and a very good adc (which I don't like much cause we need more support players, we don't need more adc players, and taking such a fun champion from support mains will be just disappointing).
Now to my point.
Currently Senna builds Spellthief's Edge, and than upgrades it to a Frostfang (which costs 450 gold), than she proceeds to buy Duskblade most of the times (2900 gold).
Current (9.22 patch) Duskblade has a passive that clears wards just like Oracle Lens, and in some way is even better (it knows when the ward is near). That passive alone is a very very good tool for keeping vision in control, denying vision on drake from enemy team, and it's a tool only available to AD supports, and only reason Duskblade on supports isn't that much OP is because it is pricey.. Being at 2900 gold + 450 gold from Frostfang/Targon's Brace.
With PBE changes, AD supports will be free of upgrading support item, and will have an access to probably best item Umbral Glaive and it's passive for only 2400 gold!
Which means, AD supports will be getting "Blackout" passive even before Oracle Lens, and I must say that is quite broken, even though item itself isn't so strong in numbers.
I'm happy that we will see an increase in AD supports, but that probably hurt AD assassins on mid lane, so we probably need more AP champions for toplane IMO. But I won't go so far with that, cause we already have lots AP mage junglers and top laners, and it's not something I want to talk about much in this topic.
Now for Senna.. She is already pretty much banned all the time (And her winrate is skyrocketing). I want to play that champion Riot... I don't want her to be OP; I can't main it if I am not able to play it, and in preseason with all the support items, and lethatily item changes, it will be even worse.
Now my opinion on Senna and possible changes I would do:
Passive - Nicely done.. I would increase number of mists needed for upgrades from 20 to 25 (which will nerf her ADC play rate because it's harder for ADC Senna to get wraith's mists, hence less range, and longer time for a power spike); (If not that, I wouldn't decrease already low chance of getting a mist, when taking cs, but instead I would make it so taking Cannon/Siege minion and large monsters as Senna has 20%-40% chance of dropping a mist)
Q - People think heal is op but I think this ability is well done, especially the part where cast range and ability range aren't the same. (heals are good.. and it makes building support items more viable, which gives champion many choices in items)
W - Probably most OP ability of them all.. Slow projectile is nicely done, but range is unexpectedly high.. (If I was to balance this ability, I would either lower it's range, or even better, make it root the target it hits, and everyone near the target gets slowed instead of rooted.. But if target dies, everyone around it is rooted instead, just like now)
E - No comment on that one, could be said a broken ability, but then again it has a decent channel time.. So kind of usable in fights, especially with flash, but if fight has already started, you could as well not be casting it, and deal damage instead.
R - Very fun ability, yet probably very very unstable in terms of balancing a champion. I like the concept, but I think it's too much.. Damage is not soo high, but for such a global ultimate I would probably nerf about 10% of it's damage.. Shielding part I do like for same reason I like her heals on q (Makes support items more viable on her)
If all those things were to be nerfed, she would probably be a bad champion overall, so yeah, those suggestions weren't as if I would do them all at once if I was balancing a champion.
Anyways hope, someone will read this all... Sorry for a long post, and have a good day.