In Tournament 8 you don't get to pick your robot and fight, instead you have to play with all your 8 robots.
Since you have to play with all your 8 robots, going for the
The Super Team achievement in Insane Robots worth 267 pointsUpgrade your 8-robot team to average health 40 or more and average slots 6 or more
will make Tournament 8 so easy you won't even need to read this guide.
There is a cheap way to beat Tournament 8 (and all tournaments) using the save trick:
You won a battle? Save&Quit
You lost a battle? Quit without Saving
You fight with 4 of your robots against 4 Elite Sentries
Elite Sentries have around 20 Health and some my have the Deep Clone augment that allows them to respawn once with around 10 health.
Exactly the same as Area 1 but this time you play with the other 4 robots you didn't get to play in Area 1
Here you will fight with your surviving robots from Area 1 and 2 against the Kernel
The Kernel has a whopping 100 health, if you have the Attack Harmony, this is not a hard battle, especially if you reached Area 3 with all your 8 robots.