This is possible to complete on Hard and Expert, and Normal.
Unit that can be used.
Psyco Gundam (A Rank)
GP03 - Dendrobium
Any MA that has high defense.Theres nothing much to it.
Items needed : optional
Skill parts (Optional, you may need it)
Release full potential ( or something it's called. It is used to maximise the unit's attack power)
For Destroy Gundam only on Hard mode. The other units can use this method as well. -------------------------
Phase 1: just keep killing, If you're using destroy. try to get all your shots to hit. PS armor helps you alot here. Use the Mode 2 to approach the boxes and since the beam reflector on the mode 2 of destroy helps on the gelgoog's beam cannon attack, it helps you and lets you be more confident. Repeat the same for all the boxes. Best is to use the homing missles and then instantly kill all the zakus. Save yourself HP.Nothing much to say other than that.Your HP may be around enough for the skill 2 to be on as soon as you finish. Happened to me.
Phase 2: simple one. Just keep spamming, wait until the Ginns reaches near the derbis. Don't waste ammo, if you're in a tight situation, it's okay to use the Reload up item. Take care of the GINN that will attack you and not the derbis. If you used Reload Up. Just go mode 2 and spam missles. You can relax for awhile if you do that, take care of the HP as well. Don't let the first derbis to be destroyed if possible. Then just wait until time is over
Phase 3: kill 20 enemies. Reload up and spam missles if possible. Change modes as soon as the ammo is used up, you need to move alot in this phase. Kill the Marasai and Hambrabi as soon as you see them. It heals the WhiteBase. Nothing much to say other than to keep spamming and not to miss. Miss the enemy too much and you may fail.