A Spanish exclusive heavy cavalry at fortress level with a Master Armourer, Master Spearmaker and Master Horse Breeders Guild. They are extremely powerful units recommended for charging straight into enemy lines.. watch any spearmen under halbedier level fall like dominoes under their long pointy lances. They are even more powerful when flanking.
Swiss armoured pikemen
These are muslim exclusive archers with pretty good mele stats. This would make them pretty overpowered, if they didn't have only 12 Men per unit. To balance that out, they have the abillity to hide themselfes everywhere as long as they stand still. This makes them exelent flankers and if proberbly used pretty dangerous.
There are 3 Janissary Units. They have in common the fact that they are exclusive Units of the Turkish and that they need a Military Academy who itself requires a Great Mosque. Since the Great Mosque can only be built once in your Kingdom, these Units are somewhat sparse. You can bypass this limit by tearing down the Mosque after the Military Academy is finished and build a new great Mosque in another Province. Note, that this will take time and may be considered exploiting, if not cheating.
The Janissary Units are:
They require an additional Master Boyer. They are slow archers with pretty normal archer Stats except a higher Moral and the Elite and Discipline Status. They shoutdn't be used in melee combat. They are the cheapest and in most players' opinion, worst Janissary Unit and you should use another unit if possible.
They require an additional Master Boyer and a Swordsmith Guild. If you recruit them in Georgia they get bonus valour. They are slow archers with slightly worse Stats than Chivalric men at arms but are Elite and Disciplined. They can be used in melee combat . They are a better version of the Janissary Archer and probably the best Archer Infantry Unit.
Janissary heavy infantry
They require an additional Master Spearmaker. They get their bonus valour if build in Bulgaria. They are fast infantry soldiers with a Halberd which gives bonus against armor and against cavalry. They have High Moral and are Elite and Disciplined. They are the most expensive but, in most players opinion, the best Janissary Unit. If you only have one Province for Janissary Units this one is your Pick in most cases.