"Bandido" (aka "Sheriff") has come up multiple times in discussion over the years. It has the annoying feature of a score doubling even though the maximum displayed digits cannot possibly be useful for lengthy performances.
Score submission possibilities in past were rumoured to be in the multiple quadrillion range but ultimately never made it to TG for one reason or another.
"Garfield" is even worse as the doubling frequency on that title occurs much more rapidly thus marathon submissions could have more zeros that the TG database could even handle. I calculated well over 10 years back when Todd was still submitting scores that he would need to play for an estimated 55-57 hours straight to achieve a score of 1000 digits in length, technically a TG milestone which was his goal.
When you say "pen and paper" is easy...sure, for 9, 12, 15 digit numbers and even a bit more. But once you enter the realm of triple digit scores good luck. Try and see how long you can double 30-digit numbers and you will get the idea soon enough.
Fortunately the threshold for "Bandido" is likely a 16-digit score so it won't be as bad should anyone pull off what at least one submitter claimed to have done decades back.