So visions reads "look at the top 4 cards of your deck".

If i only have 2 cards left in my deck (about to cycle) what happens if i play visions? I look at 2? Or since i cannot look at 4 it fizzles?

I believe this falls under the "do as much as you can" rule.

Aye, same thing was ruled for Glimpse of Fate (look at top 6, so it came up a bit more often).