1. Kennedy/Medici challenge. While remaining a republic, pass on the dogeship from father to eldest son as if under Primo and consistently keep intermarrying with the highest feudal ranks.
2. Turn the tide. Start as Cornwall in 769, which is only decades after losing Dorset and Somerset (that's in Wessex now), start getting your stuff back. Get a connection with Wales. Do some research and focus on liberating those counties that are recent Saxon conquests and/or are historically somewhat more likely to have had a surviving Welsh-speaking populace.
3. No landgrab. No fabrication of claims. No assassination. No gimmicky matrimarriage stuff. No pressing of younger brothers' claims vs older brothers in Primo counties. No interfering with elections in Elective countries unless you are restoring (the kids of) a deposed hereditary ruler. Don't use holy wars and similar CBs for mere expansion, use them always to liberate lost lands or at least to legitimately weaken a threatening blob.
4. Reverse outside bid. As Harold Godwinson, become King of Denmark (yes, he had a shadow of a claim).
5. Komnenos comeback. As Trebisond, 1) get C'ple and 2) become the official emperor of Byzzie Empire. (This is in the insane region, because you are likely to go down in 1-2 holy wars from overpowering neighbours.)
6. Marechal Foch in Asturias. 'My centre is giving way, my right is retreating, situation excellent, I am attacking.' Basically try to maintain an offensive live vs the Umayyads as Asturias. If Catholic revolts succeed, you should try and vassalize the new Catholic rulers in Spain as the rightful successor of the Visigothic Kingdom.
7. Visigothic Kingdom is back. Form e_Spain, keep Capital in Toledo, keep Visigothic culture. Try to get at least d_Toulouse and d_Provence.
8. Visigothic Provence/Burgundy/Aquitaine, i.e. the
Kingdom of Toulouse — Be and stay Visigothic, obtain the Kingdom of Aquitaine (rename it to the Kingdom of Toulouse) and/or Burgundy.
9. Republic of Ireland. Make sure Republic of Ireland is on the map. It doesn't need to own d_Ulster. Just sayin'.
10.
Llywelyn the Last. Turn 'last' from adjective to verb, and make him
last. I honestly don't know how, but control all of k_Wales before you die. You still get distinction for creating and defending k_Wales.
11. The other Matilda. Using whatever date or character you want, put the Empress on the throne of England, replacing Stephen of Blois. Doing it as a kaiser would be cool in itself but too easy to win this challenge.
12. Poland-Lithuania. Start in 1337, as whoever you want. A son of Algirdas has to rule k_Poland and k_Lithuania. Bonus if you can form the Wendish Empire (and rename it).
13. Anscarid return. Put the d'Ivreas back in control of k_Italy in 1066. Bonus if you can get an imperial title after it within a reasonably short timeframe.
14. Louis is Emperor! Start as Louis in Italy in 867 and get an imperial title within your lifetime — only HRE, e_Italia, Francia, Germania or custom title. HRE, Italia or custom title preferred.
15. Catholic Berbers. You have to start as a Berber with a Catholic capital, plausibly revert to Catholicism, hold your ground etc. Making sure that Carthage has a bishop named Augustine is not mandatory.
16. Sons of Julian. Pick either one (Tanger or Ceuta), try to undo the damage your father did in helping dismantle the Catholic Visigothic Kingdom.
17. Visigothic reconquista. Start as the Byzantine Empire's Visigoths in Mallorca. Be a good foederatus (barbaric ally of Rome). Get a Visigothic Spain back for the Roman Empire.