Floodgate vacation

Getting out in Floodgate is quite easy. On the high walls at the start, jump on top of the boxes, then grenade jump on to the walls. A texturing problem of Bungie's fault also appears here, due to them not making the rails completely "solid". Go through the rails until you reach the end of the straight line then head right. Instead of falling which would normally happen, the "floor" is flat and "solid". This makes it an easy way to escape enemies on Legendary mode as you can now finish the level without being hit.

Vacation atop the Floodship
Play the level until you get to a part where Shadow of Intent (the Sangheili ship piloted by Rtas 'Vadum) sends down 2 friendly Phantoms to drop off Elites, you will see three shipping containers stacked up like a staircase, kill the nearby flood and pick up a Deployable Cover. Go back to the containers and push a crate next to the bottom "stair" to get on top. Deploy your cover on the "bottom stair" to get to the "top stair" but don't jump up yet. Advance until you can find another Deployable Cover then go back to the containers. climb up the containers and jump onto the slanted part of the building in front of you and walk left until you get to some reddish-brown pipes coming out of a "ramp" on the roof, climb up the "ramp" until you can get up to the slanted top of the roof. Walk diagonally along the "invisible wall" toward the crashed flood ship. Don't be afraid to walk over the invisible areas, as they "exist" (you can walk on them). When you get to the place where the building you are on connects to a wall, walk to the edge of the roof. Turn around, deploy the cover, and climb onto the roof with the balcony. Now walk towards the crashed ship. When you get to the part where the roof is smashed by the ship, jump onto the latticeworks of the ship and onto the ship itself. Now you can climb all over the Flood ship!! (Be careful not to fall down to the place where the Arbiter sends you into the ship to get Cortana, as the game will generate another "invisible wall" to stop you from getting on top of the ship from the latticeworks)