Yes, hello! Heard we were talking about Tom Nook!
What I imagine is that he'd share a handful of moves with Villager and Isabelle, but his specials, throws and some smash attacks would be very different-- the Wolf to Villager and Isabelle's Fox and Falco, as it were.
There are two things Tom Nook can do that
1. Villager and Isabelle haven't done already, and
2. Are something
only he really can do.
And those are:
Bells:
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and Furniture Leaves:
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I imagine that Nook could gain more Bells the more attacks he lands on an opponent, boosting his stats the more Bells he has on hand. Basically, the anti-Lucario. Bells could simply stay in his pocket, or be spent on stronger or quicker attacks. If the player wishes, Nook can also, as others have said, spend Bells on buildings and taking over areas of the stage that would penalize the opponent if they stepped foot in it-- a literal zoner. If he has to use tools, he could even spend Bells to (possibly temporarily) upgrade those tools into their silver or even golden variants.
As for his leaves, they could be placed by Nook as part of his smashes, landing on the ground as furniture, or laid down as traps like Snake's C4, or even thrown like throwing stars, turning into furniture on impact. This might be pushing it a bit, but perhaps they could lean into his tanuki origins and have him transforms items into leaves that he can use.
Pocket, I feel, is the Animal Crossing thumbprint in Smash Bros, much like the Fire Emblem cast's counters and the Star Fox crew's blasters. Tom Nook's version can be differentiated from the other two Animal Crossers by allowing him to "sell" items and projectiles he catches and convert them into Bells to boost his stats.
And what better Final Smash for Tom Nook than building a house for his opponents, dealing massive damage from the sheer weight of the debt they've found themselves in?
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Long story short, I think Tom Nook can make for a very interesting character that, while similar, can provide a different experience from Villager and Isabelle. If another Animal Crossing character is on the table, it's probably going to be him.
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