Verb-
from Casper the Friendly Ghost-
To make something easy to understand and comfortable(i.e., transparent and friendly) that would otherwise be difficult and scary.
Making General Relativity easy to understand by dressing up like Einstein and providing very simple and tangible examples. "I wish someone could Casperize calculus for me; I have some kind of mental block against understanding it".
A phenomenon that occurs when a video game developer changes a game mechanic to make the game easier for new players. Alternatively, if a game developer lessens the skill gap, then this phrase fits the mould as well. This typically makes the game less enjoyable over a longer period of time