Rotating game mode: Friendly Fire ON.
Teamfights are already really chaotic. But what if you can't just spam your AOE onto the group without thinking?
Introducing Friendly Fire: On. The new rotating game mode where you can hit and kill your allies.
Friendly kills would count as executed, so if an enemy champion has dealt damage to them recently, they'll receive the kill. (No champion-denying here. Unless they were out of combat.)
Perhaps even turn on friendly fire to minions so we can deny those. Riot should playtest this and see how this would impact the fun of the game. (I can imagine it could be very frustrating, but also hilarious at some points.)
Does she heal her allies, damage them, or both at once?
Help, Pix!
...
I said help, not kill!
I'm
here
to
help
you
I
swear
that
this
won't
go
poorly
at
all 
R.... The true 1v9.
I'm not seeing what changed here exactly.
:

: What's that? Go for the Decakill? If you say so.
+
+ Passive + E
, and his Pick a Card ran out after choosing one, it would do the damage to TF and if he was low enough well.. I think you get the picture.
,
,
,
,
ult.
getting five stacks on one ally before battle, runs in with full stacks and kills everybody.
Hook like a Thresh lantern, without the stress of CLICK THE LANTERN.
Cast ultimate on a mobile team mate, who runs behind enemy squishy.
Get health from your team! Then Heal your team using that health!
Boop. Headbutt your squishies to safety, or your juggernauts into enemy team.
Heavy panting at thought of stacking own minions. Or wards at fountain.