This isn't something that I can't control that OMG I DO ALL THE TIME, but sometimes I'll be some places or in open areas and imagine ? blocks floating everywhere and coins scattered everywhere, for instance. I always imagine (when I'm walking a far distance) how fast I'd be going and what path I'd take if I got the Rainbow Star from Galaxy and was running at like... what 15-20MPH. I imagine mowing people over and cars flying up and shaking like they do if you hit them in Double Dash/MKWii/DS with a star with the familiar sound of impact (since Double Dash) sounding like a PPK with a suppressor on Goldeneye [007] ..and I always think what if I could seriously jump as high as Mario or Luigi... or had Smash Bros. physics and all I had to do was wiggle my arms in circles and be able to jump off anything. Do you know how useful that would be?! And to be able to punch and do Over+A and have my fist become as large as a beach ball [like Mario]! I'd hit everything! I've always wondered what being in a pipe would feel like (Mario-wise, obviously) and also how cool it'd be to have them in real life. Is it a vacuum like the banks use for their drive-thru? Being invisible would be really awesome too!
That was my old reply. Edits are in italics so it's a little more coherent.
I still basically think the same thing. Smash Bros. physics would still be awesome because I'd go jump off everything and just wiggle my arms in circles to slow down. Jumping as high as Mario (or Luigi, actually) would be extremely useful. A double jump and an Up+B Super Jump Punch would be even more awesome. I still imagine myself plowing through people and vehicles with a Starman. I'm actually making an animation about that.
One thing I forgot to mention in that old post is that after playing Road Rash 64 so much, I'd always play the lyric-less songs in my head from the game when I'd ride with my dad on his motorcycle way back then.