Rek'Sai Tunnel Glitch
I found a bug with Rek'Sai's Tunnels that caused it to stay on the field indefinitely. This Tunnel could be Ulted too and freely used. It didn't count towards my Tunnel counter on my ability bar.
Here is a picture that showed the glitched Tunnel. The cooldown bar is completely black yet it does not disappear. You can also see 2 other active tunnels on the field (both in my base, one over our nexus and the other near the top) yet my Tunnel counter only lists these 2.