This is not real. From 0-12% dthrow into shine is real on all DI that isn't away. On away DI though you can regrab if they do not perfect buffer spot dodge or shine. DI/SDI away and then asdi down to shine to stop falco from comboing you.
After 12% fox can just hold down and shine you before you can shine him.
you can just pummel once dthrow regrab pummel backthrow regrab pummel upthrow it's pretty sick since if they're trying to escape a second dthrow regrab they get di trapped into the regrab, pummeling ****s with their ability to focus since no one does it, gives you free %. You can also hard read DI out and dash jc grab (same timing as shinegrab if you're worried about the timing being possible) before they can act too.
But you could also space a dair and get 12% for free and not play some overly thought-crafted semi-optimized read-based grab game, and just use your grabs for gaining stage control which would set up for more dairs and potentially a stock.
are we in an alternate universe where you can't tech dthrow?
Fox's stats for weight and fall speed are somehow perfectly balanced in NTSC to make Falco's dthrow untechable by Fox specifically (people say he touches the ground while in the grabbed state and bounces up from a laser impact), but he can shine you out of it and most foxes know to do so. If you're playing against a new fox and you dthrow and see a shield pop up, they either forgot about the shine at that moment or don't know, at which point I personally would keep dthrow regrabbing them forever until they shine you or escape out of desperation, then move onto something else. As other people have said, in PAL his stats are changed so dthrow regrab is no longer possible.
The 20XX 4.05 cpu doesn't know how to deal with this though, since it DIs in a random direction, so you can just dthrow chaingrab 20XX cpu fox until it eventually (fully randomly) waveshines you into a 0-death or otherwise breaks out by DIing behind you or out too far at higher percents.