Penta killing needs more love :o
Like, an in-game mini triumph theme right after you or an ally did a penta, only heard by your team?
A simple crowd cheering or something more sophisticated like https://www.youtube.com/watch?v=_sf0C-0YonU
Or an existing League theme shortened? https://www.youtube.com/watch?v=orOy9W0b1kE
Also, a theme for the ones that just received the penta. This might be salt on the wounds though :/ https://www.youtube.com/watch?v=vNwsFT_MJjs https://www.youtube.com/watch?v=hpVkV4D64fA
And finally, an achievement introduction! Get X amounts of penta kills in ranked to be rewarded with, let's say http://i.imgur.com/SkAbWjA.png an icon. Even more pentas http://i.imgur.com/xJH7xdG.png a crest!