Simple death fader for GZDoom. Put both files into a .pk3 or .wad.

mapinfo.txt

GameInfo {
	AddEventHandlers = "DeathFadeBootstrap"
}

zscript.zsc

version "4.1"

class DeathFadeBootstrap : EventHandler {
	override void PlayerDied(PlayerEvent e) {
		PlayerInfo player = players[e.PlayerNumber];
		player.mo.GiveInventory("DeathFader", 1);
	}

	override void PlayerRespawned(PlayerEvent e) {
		PlayerInfo player = players[e.PlayerNumber];
		player.mo.TakeInventory("DeathFader", 1);
	}
}

class DeathFader : Inventory {
	int counttoblack;

	override void AttachToOwner(actor User) {
		super.AttachToOwner(user);
		counttoblack = (owner.health + random(5, 20)) * 35;
		counttoblack = max(counttoblack, 10);
		owner.A_SetBlend("black", 0.0, counttoblack, "black", 1.0);
	}

	override void DoEffect() {
		if (counttoblack <= 2 && owner.health <= 0) {
			owner.A_SetBlend("black", 1.0, 5, "black", 1.0);
		}
		counttoblack--;
	}
}