Please check out the Original Mod:
https://www.nexusmods.com/divinityoriginalsin2/mods/99

This mod sets the Vitality, MagicArmor and Armor of Bosses to 200%. (Double HP, Armor and MagicArmor)

This is a copy of the Mod by Reveurr with tweaked Numbers.

I also added the following bosses:

CoS_Spymaster - The Shadow Prince
CoS_AutomatonBoss - The Great Guardian
CoS_SallowMan - The Sallow Man
EG_Braccus - | Braccus Rex |
EG_Lucian - |Lucian, the Divine|
RC_Humans_Melee_Strong - The Spirit of Linder Kemm
CoS_MotherTreeBoss_Caster - Dryad of the Mother Tree
CoS_MotherTreeBoss_Ranger - Dryad of the Mother Tree
CoS_MotherTreeBoss - | Elf Scion |
TUT_TopDeckMagister2 - Captain Kalwyn
ARX_Isbeil_Summon - Isbeil
CoS_Alexandar - Bishop Alexandar
ARX_Humans_Caster_Strong - Karon
ARX_Kemm_Undead_Summon - Lord Linder Kemm
EG_Braccus_Strong - | Braccus Rex |
EG_Kraken_Strong - Kraken

# Update 2018-04-14
Added the following Bosses i found in the Patch Files:

Animals_Frost_Dragon - Black Dragon
Animals_OilSpitter - Oil Boss
Animals_Voidwoken_Kraken_Tentacle - Kraken Tentacle
Creatures_Troll_A - Kraken
CoS_AotO_SourceTitan - Source Titan
EG_Kraken - Kraken

I'm pretty sure i included all the bosses now, but in case i missed one, tell me and i will look into it.

The Bosses will have missing health if you have already encountered them ingame.
They should have full hp if you haven't encountered them yet or if you start a new game.
The Screenshot is from Tactican Mode.

The Numbers are generated by a Script and not by Hand, so they should be correct, unless i made a mistake with the Script.
Tweaking the Numbers to 150% or 300% is very easy to do with the Script, so if there are no more Bugs with this Version then i can Upload another Version with other Percentages.