trying to get enemy of my enemy achievement

hi im trying to get the enemy of my enemy achievement and killed all the forerunners and my team to prevent them from killing the elite general, and he gets close to the top but will never actually go to the top neither will he become an ally, im doing this on heroic as the achievement says to do, and i also play with the IWBYD and grunt birthday party skulls, is there something about these skulls that change it all iv also tried completing the achievement with neither on but seem to have no luck i know its the general because he has the gold armor and hes meant to become an ally but none of that is happening in my case

long time halo fan, player, just dont understand as to why this isnt working if anyone can give me specific instructions it would be greatly appreciated

When I did it, he killed me a quite a few times;

to my knowledge he never actually becomes your ally.

you just have to kill everything before he gets to the top, you just have to be super quick …

I did it solo but would be easier with a party!

**edit i also did the achievement on Heroic… **