Most Summons in Final Fantasy VII Remake are obtained either through advancing in the story or by completing Battle Intel Reports for Chadley.
However, one Summon — Chocobo & Moogle — requires a bit of work, as it can be easily missed in the course of the story. Here's how to avoid that happening.
Chapter 6 Walkthrough: How to get Chocobo & Moogle
Once you have switched off all three Sun Lamps, don't use the large cargo elevator just yet.
Instead, head west to find a smaller elevator that leads to a ladder on the wall with the giant vents you climbed past at the beginning of this section.
In the first room, you can use the Vending Machine to pick up Music Disc #18 — Electric de Chocobo.
In the next room, activate the terminal. This will start a 60-second timer — you now have to defeat the enemies in the next room and use the terminal on the far side before this timer runs out.
Should you fail, don't worry — just go back to the first terminal and activate it again. The enemies will also be easier this time!
Once you've done this, the terminal will announce 'Maintenance Mode' is activated, and you can pass through the door into the vent to collect the Chocobo & Moogle Summon Materia.
On Hard difficulty, you'll be able to pick up the Way of the Fist Vol. VI Manuscript from the same location, granting Tifa extra SP.
