To conserve Mana, I remove all spells with maintenance cost while building up for the next war.
Then when war starts, I want to apply a lot of spells at once.
That takes a LOT of clicking in FE/LH. Way more so than any feature in any other PC game I've ever played. (With the possible exception of games ported from a console platform, which have more limited user interface forcing more steps.
What seems to be missing is the awareness that once a user starts doing a certain action, they are likely to want to do more of that action.
An easy change that would help this situation:
REMEMBER the previous state of the Spells window.
Example: User clicks "Spells". Then "Unit Spells". Then scrolls to 3rd page. Then "Stone Skin". "Cast Spell".
After selecting the army, and unit, now wants to repeat.
THIS time when clicks "Spells", the window could come up, AUTOMATICALLY activate "Unit Spells", and scroll itself to 3rd page, and (itself) highlight "Stone Skin".
Now all I have to do is "Cast Spell", and I get the same spell again. Two clicks instead of six.
Equally useful, if I instead want to cast a different unit spell, I am already close to what I want. Just pick the one I want, perhaps changing to a different page.
Contrast that to the current situation, where I have to repeat every single step I did the first time. Once I have a lot of spells available, this becomes tedious.
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Another common desire is to cast multiple spells on the same hero. The above change helps this too, because the window would already be showing the list of unit spells, and the next one wanted might even be on the page being displayed. Three clicks instead of six.
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*UPDATE* I see that this is mostly implemented. Unlike original FE, when go back to the Spell book, the previous spell is selected. I didn't notice this because ( a ) I was so used to the previous version, that I had a habit of immediately clicking on the "Unit Spells" button, ( b ) It is in "All Spells" mode, not "Unit Spells" mode. So the list of spells shown isn't what I was expecting to see.
Good enough. Now that I know to unlearn old habit, and pay closer attention to what is showing!
IMHO, would be even better if it remembered I was in "Unit Spells" mode, so that I would be right back to where I was before. But that is a minor nit.