Death messages are being updated for 1.13, and some of them are still a bit barren.
You may suggest messages for any situation, but I'm specifically looking for:
Blaze:melee(2)
Blaze:fireball(2)
Blaze:Burning(3)
Cave Spider(3)
Creeper:Blown off a cliff(1)
Drowned:Melee(4,re-uses some from zombie)
Drowned:Drown while fighting(3)
Drowned:Trident(1)
Guardian/Elder Guardian(4)
Drowning whilst fighting Guardian/Elder Guardian(1)
Ender Dragon:Melee(3)
Endermite(2)
Evoker:fangs(2)
Ghast:fireball(2)
Ghast:fire(1)
Ghast:burning(1)
Ghast:Blasted into lava(2)
Ghast:Fall damage(1)
Husk(2)
Polar bear(1)
Shulker(3)
Skeleton:Melee(2)
Stray:Melee(2, uses same as skeleton)
Vex(2)
Vindicator(2)
Witch(1)
Wither:Explosion(2)
Wither:direct damage(2)
Wither:Wither effect(0)
Wither Skeleton:Melee(2)
Wither Skeleton:Wither effect(1)
Tamed Wolf(1)
Zombie Villager(only 1 unique from zombie)
Running into a cactus while fighting something(1)
Drowning while fighting something(2)
Elytra:Flying into a wall(4)
Elytra:Flying into a wall when fighting something(2)
Falling:Out of water(1,possibly unused)
Falling:Onto a cactus(1,possibly unused)
Falling:Onto a fire(1,possibly unused)
Falling into lava while fighting something(3)
Channeling Trident(1 unique from normal lightning)
Suffocation while fighting(2, though this situation is rare)
Squashed by an anvil while fighting something(1, though this situation is rare)
Fireball(2, this should only happen when being hit by fireballs shot by dispensers)
Potions of harming(3)
Wither effect(2)
Additional the death messages will support the following conditions:
LOST_DIAMOND:Showing how many diamonds/iron/string/feather were lost on death(example "(Player) watched a wither explode their (items)."
AFK:Shows while the player is AFK
END:Shows in the end
NETHER:Shows in the nether
NIGHT:Shows up at night
MINING_NO_DIAMOND:Shows when mining near diamond level
BROKEN_ELYTRA:In case you want to make a message for when somebody breaks their elytra and falls to death(we already have a fair amount of these, but if your suggestion is good it'll be accepted. this can also be combined with LOST_DIAMOND and NIGHT)
FLYING_ELYTRA:Shows while flying with elytra
PVP:Shows both the killed player and the player that killed them. This can also be combined with LOST_DIAMOND
Added:
supahgamer2's "got an F in chemistry", "got in a breath holding contest with a Guardian and lost", "tried to firebend", "should've bought ACME", and "lost the high ground"
neicey69's "couldn't bear the pain", "made an emergency landing"