To quickly kill Repta in the first encounter, first equip your pistol before stepping into the arena an select the shock grenades as your grenade. You will need a pistol because you can throw grenades at a faster rate with it. Find Repta and go on the same catwalk as he is on. Precisely throw a grenade at Repta. Make sure it does not fall off the catwalk. When he is stunned, quickly switch to satchels and throw two (recommended) or three satchels at him. Once they are stuck onto him, immediately switch to your Nano GL and shoot a round at him. Do not stand too close. Repta should lose about one third or one fourth of his life. Repeat this if desired for an easy kill.