The vines grow around the edges of the screen when Wither damage is taken. Nasty.
Just in case you weren't aware you were on fire, this will pulse in and out. Also looks nice compared with the Frost Overlay.
The Damage Overlay in action. The direction of the damage, (in this case, the front), determines which way the overlay appears.
Different potion overlays appear in different circumstances. The Regeneration Overlay pulses whenever the player heals with the potion.
The effect is subtle, but the screen edges gradually get darker as Oxygen runs out.