It first happened in the video above. As an Illaoi main and [bug tester](https://boards.na.leagueoflegends.com/en/c/bug-report/2Ncw9ex9-illaois-50-bugs-updated-list) i started checking what went wrong.
The tentacle attacks two times.
It attacked once.
I first tried to reproduce what happened in the video, so after spamming my W at an almost dead spirit for some time in practice tool i finally understood what went wrong. https://youtu.be/_bHMJZxaV2M
Basically my tentacle killed the target, and then my W attacked it. To not include the spirit in my reproduction because it acts strange sometimes, i decided to do it against monsters and it worked. https://youtu.be/XMGBEXrMSio
This shouldn't happen because W usually cancels without going on cooldown if the target dies before attacking it https://youtu.be/ONvdb7py5a8
There are two different solutions for this:
1. Make W not cancel itself and still hit even after the target died, but still trigger tentacle slams.
2. Make W cancel itself without going on cooldown upon hitting a target at the same time it dies.
Ps: this may be a general bug, because a lot of times, when i simply farm with a melee champion, the minion dies and my attack still goes through, thus going on full delay (i'm not able to attack another minion for some time with low attack speed)