So, Robin's custom moves. Some ideas.
His down special could involve him using other dark magic spells.
Mire could be a long distance version of Nosferatu (grab special) without the healing part.
Ruin would be a blast of darkness with a certain sweetspot for massive damage, but weak otherwise. Kind of would replicate the tome's original high critical ratio, but weaker power.
His side special custom options could be Dying Blaze, a very powerful fire spell that would wear out faster than usual (assuming each elemental tome has its own durability). It could cause a huge explosion of fire in front of Robin, having a rather large hitbox. Would be an intentionally relatively overpowered move, but impossible to spam due to its low durability. To reinforce its high risk, high reward idea, it would be slower and leave Robin vulnerable.
The other option would be Bolganone, which would cause an eruption of lava, launching foes upward. This could be used as a start up for aerial combos.
As for his up special, Wind would be weaker but would allow Robin to recover easier, while Arcwind would trade recovery ability for power.
For his neutral special, Bolting would keep the same charge mechanic as the known default one. It could consist in a lightning bolt that would appear from a certain distance from Robin. The more charge, the farther it would appear. Charge would have no bearing on its power. This tome didn't appear in Awakening, but is still a recurrent tome in the series.
The other option could be Mjölnir and it would also involve charge. The spell would consist in a blast of lightning whose radius would be bigger the more charged the move was.