Entity Outliner
Updated for 1.19!
Entity Outliner is a clientside mod made with Fabric that allows you to select entity types to outline, making them visible through obstructions within render distance.
Features
Entity Selector

This screen allows outlining of any entity in the game. There's a search bar for narrowing down entities and buttons to organize the results by entity category, deselect all entities, and toggle on/off the outlines. Entities added by other mods appear in the results. The selected entities are automatically saved to a config file.
The menu is accessible using
Mod Menu or a custom keybind.
Controls for toggling the outlines and opening the selector

Custom keybinds are provided to open the entity selector and toggle the outline. The outline can also be toggled via a button inside the entity selector.
Screenshots
This mod will help with:
by outlining them.

by outlining zombies/creepers/skeletons/spiders.

by outlining them.

- Finding your death location
by outlining items and experience orbs.

- Wither skeleton skull hunting
by outlining wither skeletons

by outlining chest minecarts and cave spiders.

And many more!
Installation
1. Install Fabric
2. Drop the Fabric API jar into the mods folder
3. Drop the Entity Outliner (and optionally the Mod Menu) jar(s) into the mods folder
Compatibility
Works with MobZ and Optifine. Let me know if you find any compatibility issues.
License
MIT. Feel free to use this mod in any modpack.