Singleplayer Lagging Like Online Lags And The Zombies Head Are Black

Well, Hello There!

I noticed a lot of lags on the singleplayer... The lags are rollbacks, game's mobs stop moving and blocks that I break are not dropping... Then, sometimes, the game goes back to normal but it's kinda getting on my nerves because I want to play my survival game but I can't because of these sort of "lags" that looks like lags that you find on Multiplayer when you have a bad connection...

 

The Second Problem (Less Important)

The second problem is that the zombies have a black head... And it's funny but I would like the normal zombie head back, please