It can flow 5 blocks from the source at a speed of 1 meter per 18 ticks. When a player gets in contact, their movement capabilities become very limited and the player gets Poison III, Weakness II and Mining Fatigue II as long as they stay in contact with the fluid.
When in contact with water, the Ender Goo tries to consume it. In the End dimension, the Ender Goo usually succeeds very quickly and after the process, it disappears for the most part. In the Overworld, the power of Ender Goo is highly reduced, thus the goo will usually fail to overtake the water.