Great ideas!
1: Yeah that cat game sounds really fun :)
2: Great idea, like how Zelda 64 Majoras Mask worked.
3: I had the same idea too, at least for the swords, or just make more shots for each gun character. I will talk about my Lode Sword idea in a second.
4: Uh, this one seems pretty hard to imlement, but if you are talking about just play the parts where your character (frog for example) plays then yeah, that woulden't be to bad to imlement and would be fun.
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Now my idea, I talked about this a little before but not in much depth.
The Lode Sword is defently one of the most important swords in the game, considering it is in all origional Chrono Art and Crono seems to have a certin bond with it, I was thinking that Crono always has 2 Swords, your one current cool sword and the Lode Sword.
My reason for this is that for spells/special moves/movies it would be much better to have a consistant sword that chrono uses for special things for the sake of saving time and consistant look.
I was thinking that Spekko would tell Crono (just a one-liner, nothing to change any story) that the Lode sword is a special sword that chrono bonded with emotionly, mabey becacsue he slayed his first boss with it (the Mechinical Dragon). This would make him always carry his Lode Sword and his Current sword.
So for say, Spire, the attack where chrono plants his sword in a enemy and strikes it with lighting, he would use the Lode sword for the attack istead of his current weapon that may look wierd.
Thats another reason for this, the Lode Sword is a very old and triditional sword, the standard of a Saber for the time, in some situations it would look better than a funky demonic special sword.

By Guardian of Ages
Here is a picture of Chrono with 2 swords, See how that Lode Sword is a nice looking standard sword, where as the one he uses for normal attacks is on his back.