Severe graphical problems such as 16x16 chunks of world textures meshing together and sporadically shifting back and forth in rapid succession, being miss-assigned to mobs and appearing uniform across multiple chunks. Edit: Exact replication in fresh generation of the world I first saw this on gave me the same results as the first encounter.

What I expected to happen was...:
The game to run smoothly, as is the usual case would be.

What actually happened was...:
A graphical glitch, as explained above. Different meshes seemed to blink back and forth as the player moved. This did not fix itself by exiting out and re-loading the world; this actually made it worse, as no chunks loaded, but the graphical glitch persisted, and blinked with different textures, such as the textures for items like the clock, carrot on a stick, etc. This persisted throughout multiple worlds, newly made and previously made. There were no missing textures displayed. Edit: This appears consistently when done by the steps I list. Further experimentation shows that it gives the graphical bug to other worlds, but is not permanent. The created world will always carry this bug.

Steps to Reproduce:
Edit: These exact steps re-create the effect every time to my experience.
1. Run snapshot 16w02a
2. Click single player, create new world, more world options
3. Set world type to Custom, click Customize
4. Set it to "Caves of Chaos" preset
5. Using the first page of world alteration, make the following changes
--a. Sea Level 70
--b. Villages: Off
--c. Dungeon Count: 100
--d. Water lake rarity: 10
--e. Lava lake rarity: 10
--f. Biome size: 6
6. Click done, enter the seed "Obscuro"
7. Generate

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(on new world, first [and only] occurence)
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