So this is an pretty simple request, when you use the damage entity procedure block, there should be a drop down to choose what type of damage that it is dealing.
So, lava damage, cactus damage, void damage ect. this is used to set the death message and immunities
For example
entity.attackEntityFrom(DamageSource.GENERIC, (float) 2);
Changed to something like this for lava damage
entity.attackEntityFrom(DamageSource.LAVA, (float) 2);
Here is a list of all damage types in the game as of 1.12.2 (I think)
IN_FIRE
LIGHTNING_BOLT
ON_FIRE
LAVA
HOT_FLOOR
IN_WALL
CRAMMING
DROWN
STARVE
CACTUS
FALL
FLY_INTO_WALL
OUT_OF_WORLD
GENERIC
MAGIC
WITHER
ANVIL
FALLING_BLOCK
DRAGON_BREATH
FIREWORKS
Now, there is another thing that I would like to request that is far more difficult, which would be making custom damage types (would probably be a new element)
But I haven't really figured how I would go about doing that so that is all I have to say
It would allow us to add the death messages and maybe a procedure on death if that is possible
By the way, there is some other interesting stuff you could probably take a look at in regards to custom damage sources
net.minecraft.util.DamageSource in the forge src
This is already possible. I will consider adding a damage source selector to the deal damage procedure block.