Found at /assets/Common/Battle/BG/025_NiflTempleChapter8/Default/Sprite.png, this appears to be a map background placeholder of sorts.
A Face FC file found at /assets/Common/Face/ch00_15_Yurg_F_Normal/Face_FC.png. It resembles Alfonse: Prince of Askr.
/assets/Common/Face/ch01_27_Katarina_F_Normal/old_Face.png, Katarina: Wayward One's old Face file where she appears thinner.
Located in /assets/Common/UI/ShadowCutin/CutIn_P_C_NoName/Face_C.png
Placeholder image for a skill icons in the /assets/Common/UI/Skill_Passive1.png spritesheet before every slot filled up. No longer used as a placeholder, at an unknown time the passive spritesheets transitioned to using the empty passive icon is used as a placeholder instead.
Unused mockups are found in /assets/Common/Unit/.
Found at /assets/Common/Wep/wep_ar.png, this appears to be an arrow mockup.
Found at /assets/Common/Wep/wep_ax.png, this appears to be an axe mockup.
Found at /assets/Common/Wep/wep_bw.png, this appears to be a bow mockup.
Found at /assets/Common/Wep/wep_dg.png, this appears to be a dagger mockup.
Found at /assets/Common/Wep/wep_lc.png, this appears to be a lance mockup.
Found at /assets/Common/Wep/wep_rd.png, this appears to be a staff mockup.
Found at /assets/Common/Wep/wep_sw.png, this appears to be a sword mockup.
Found at /assets/Common/Wep/wep_mg.png, similar to Élivágar, but with a blue cross where the mini unit would hold the tome.
Found at ch00_07_Surtr_M_Normal/tex/wep axXXX_シンモラ.png, this appears to be a prototype sprite of Sinmara.
Found at ch04_00_Chrom_M_WinterFes17/tex/wep_axXXX_プレゼント袋.png, this appears to be a prototype sprite of Sack o' Gifts.
These skills are skills that are present in the game files, but are not used or have properties that are never used (e.g. the skill in the special skill refine of Camilla's Axe has usage restrictions so that only cavalry and flying units can use it, but this is never seen since no other unit can use Camilla's Axe).
Skill with no name or any properties. It cannot be forged, and does nothing when used.
For most exclusive skills such as Sacae's Blessing, the list of allowed movement or weapon types usually contains every single type instead of just being empty (as SID_無し is) or minimally having only the Hero's weapon type and movement type. However, some do not have a full list and exclude certain types of units despite never being inheritable. These are also likely an indication that these skills will only ever be released on units that match its restrictions.
Only weapons that do not allow all movement types are listed.