Issue Description
No potion effects are applying to any mob

Reproduction Steps
Steps to reproduce the behavior:

1. Enter a world
2. Spawn any mob that will be affected by poison
3. /effect @e minecraft:poison 10
4. The mob is not hurt by the poison

Expected Behavior
Minecraft's normal potion handling should not be affected except for wolf hunger

Version Information:

• OS: Windows 10
• Java: jdk1.8.0_261
• Minecraft Version: 1.12
• Mod Version: 1.12.2-3.6.3-universal

Additional Context
Likely due to the potion mixin / event handler