Blackguard

gets additional Smite Good use at each 5th level
Blackguard gained new feat at level 3 - Aura of Despair: -2 saving throws to nearby enemies;
has spellbook, spell selection is similar to paladin, needs wisdom 10+spell level to cast spells
feat Epic Fiendish Servant removed from game, now the summon from this feat will be gained automatically at lvl 15 of blackguard
all blackguard summons now get these traits:
1. Improved Evasion
2. Spell sharing (see Wizard class changes above)
3. get Blood Bond feat at character level 16+ - +2ab, saves and skills anytime the master is in combat
4. get SR equal to master's BG level+5 at character level 19+
5. All BG summons now gain extra (uncapped) stats according to the table at: https://www.d20srd.org/srd/prestigeClasses/blackguard.htm + the informations at Epic Blackguard page
6. the level scaling will now bring Epic Vrock to the same level as is master's BG level (in vanilla it has -4 adjustment for some reason)
A paladin that takes any blackguard levels becomes a fallen paladin. As such:
- can no longer level up as paladin
- loses access to the smite evil feat
- loses access to the paladin spellbook
Paladin and blackguard levels stack for the following:
- divine grace and dark blessing saves bonus
- lay on hands heal
- smite good uses
- fiendish servant level
- caster level of blackguard spells
- sneak attack damage
The saving throw bonus from dark blessing is limited by blackguard (and paladin) class levels.