I took a break from Halo 2 Legendary for a while because of IRL stuff, but today I decided to give Regret a go. It actually wasn't that bad. I was able to bring two Marines from the start of the level to the fight against Regret because I armed them with snipers and they helped a ton. I was able to clear it in about 40-45 minutes, which I think is good for what I consider to be the second hardest level in H2. I am terrified for Gravemind though.