Well, this is tricky because if Nintendo game away some IPs it would lose a lot of characters from Smash Bros. and Mario Kart, two of its best series.
OK, how about this...
1) Star Fox to Microsoft, with the understanding that the series will be developed by Yukio Futatsugi.
2) In exchange, Banjo-Kazooie to Nintendo EAD.
3) Ratchet & Clank to Retro Studios.
4) In exchange, F-Zero goes to a resurrected Sony Liverpool.










