Anyone know a way to stop/reset a mob's downward momentum?

[crafter]

Blah blah explanation, blah blah XP grinder. But I can't use vines because the mobs will catch on them and climb, cluttering the system. Anyone know a way to make mobs drop down to an exact health after already started falling?
EDIT: I tried flowing water that is as thin as it gets with a sign underneath. Mobs will still catch themselves on it sometimes but when they bounce up they fall through after.

 

[Danni122112]

Water + signs?

 

[Omar_Sales]

Have you tried resetting minecraft?

 

[kuilin]

Dispenser with water bucket and redstone that pulses it? Or lava bucket

 

[Lord_Dust_Bunny]

Blah blah explanation, blah blah XP grinder. But I can't use vines because the mobs will catch on them and climb, cluttering the system. Anyone know a way to make mobs drop down to an exact health after already started falling?
EDIT: I tried flowing water that is as thin as it gets with a sign underneath. Mobs will still catch themselves on it sometimes but when they bounce up they fall through after.

Solid water + signs seems like the best one, though I'd recommend pushing each layer (safely) down one layer, until they're all at the bottom. Probably a better way then that though.