EDIT:

I watched u/Sinzar_'s JP Wicked Moon clear where he brought a ~10.4m SPR eHP DFina who died to the double fixed magical attack on the 70% threshold. 10m SPR eHP is likely not safe to survive this threshold depending on your buffs. At sub 40% and especially sub 25%, you'll be hit with 2 uncoverable magic attacks on some turns so that 70% threshold acts as somewhat of an eHP check on your team.

According to this spreadsheet created by u/togeo, you would need >12.4m SPR eHP along with 130% stat buffs and 50% general mitigation to survive the double fixed magical attack turns assuming no Guts passive.

(Edit: Note that magical mitigation doesn't matter here since the Attack type is Fixed and the Damage type is Magical, meaning only general mitigation applies. See here for more info. You'll still want to bring magical damage mitigation for other attacks.)

Thanks u/liang_se for sharing the spreadsheet.

I'll update this post if I find out more info.

Disclaimer: These types of builds might take a long time to run. Mine has been running for about 3 hours with 2 pinned items. This post is aimed towards people who want a truly min/max unit for the trial and are ok with letting the builder run in the background for a bit.

I've seen a few posts where people recommend gearing their companion units for 10k HP 1k SPR for Wicked Moon.

However, rather than prescribing specific SPR and HP stats, it's likely optimal to let the ffbeEquip Builder do the work for you.

eHP definition: eHP is your HP multiplied by a defensive stat (such as DEF or SPR), giving you your effective (e) HP against a specific damage type. 10k HP * 1k SPR = 10,000,000 SPR eHP which means you can take 10 million unmitigated damage checked against the target's SPR before dying. Things like breaks or mitigation buffs will also affect your eHP.

Companion unit requirements:

• >12,400,000 SPR eHP (or SPR * HP > 12,400,000) if you want to survive the double fixed magical attack (see edit at the top)
• Confuse immunity Not needed per u/Sinzar_ as provoke overrides the targeting mechanism
• Maximum damage

You can let the builder build toward these exact parameters by using the following steps:

1. Log in to your account and update your inventory
2. Select the unit you want to optimize
3. Select the correct target races (demon spirit for Wicked Moon)
4. Click Custom Goal, to the left of the Maximize field
5. In the Maximize field, type in "m_damage" for magical damage
6. In the With field, type in "spr*hp > 12400000" (see edit at top) to set a minimum SPR eHP
7. Pin a few items! This is important if you don't want the optimization to take hours; Useful things to pin are Leviathan, the unit's TMR/STMR, and other really good items for this build (Light's Vengeance, etc.)
8. Click Build !

This will cause the builder to always maintain a minimum of 12.4 million SPR eHP while maximizing your magic damage output, including appropriate killers. You might be surprised at some of the weird stuff it pulls from your inventory to hit those parameters.

Shout outs to /u/CottonC_3939 for reminding me about building for SPR eHP this morning and much love to u/lyrgard for the invaluable tool.