One of the lesser used techniques for strong passwords is to use patterns or even straight up repetition, so it can be very long while still being memorable.
0110-3223-5445-6776-9889 increment parity 20
0 0 1 2 4 7 12 20 33 54 one less than fibonacci
after 3. is 14159 then 26535
11111119 and 19999999 are primes
aall leetttteerrss aarree ddoouubbleedd eexxcceepptt l
Not the best examples but you get the idea. So an actual password might look like this:
primes 235 LuA: LualuA LualualuA LualualualualuA
Looks easy for humans, but the guessing algorithm surely doesn't know the connection between
235 and the repetition of
There's a lot of patterns to work off of and a lot of possible mappings/mutations. Mappings can be layered as well. Words can then be inserted, and short prefixes and suffixes added. If the search space still wasn't large enough you could concatenate two of these to square the number of possible passwords. Is it practically unguessable or do these patterns weaken the passwords enough for specialized algorithms to be able to guess them easily?
Their length and usage of non-words should make them immune to any existing password guessing methods as well, so at least they have that benefit.
Extra: how much guessing entropy is actually in one of these passwords? There's not really any data to work off of but we could use Fermi estimation to get somewhat close.