The Night Portal
Portal 2 and 3 had the very same sealed door and Gara had decided to send his elite troops in to test Portal 2's sealed enemy and thankfully, the very same squared scaled lizardman came out. While Jin could not give them instructions on how to kill it, they immediately understood that electricity is one of its weaknesses.
However, by discharging electricity through an all metal arena does provide its downsides too and they had to use that element carefully to ensure that they did not kill their own people or themselves. And the caution given was also because none dare to lose their lives in such a simple dungeon. This was also because Jin had given a 'casual' order to state that if anyone who lost their life in the dungeon due to stupidity would have their entire family executed as well.