Pitot Static Errors
Blocked Pitot Tube Errors
If your pitot tube becomes fully blocked it will over-read in a climb and under-read in a descent. It will act like an altimeter as the static port is now its only source of information.
If your pitot tube becomes partially blocked you will see an airspeed somewhere between 0 and actual.
Your static port instruments will continue to function normally.
Blocked Static Port Errors
If you have a blocked static port all three of your instruments (ASI, ALT, VSI) will stop working correctly.
Your altimeter will freeze at the last altitude, your vertical speed indicator will settle at zero, and your airspeed indicator will under-read as you climb and over-read as you descend.
How to Remember
Just remember that your ASI will act like an altimeter if the static port is its only source of information. Your ASI uses the dynamic pressure (always changing) from your airspeed, minuses the static pressure at your altitude, and subsequently produces your airspeed.