Im making a death run map and I have an area where a lava wave comes and tries to outrun the players. Example:

. So how do you make the lava appear and then disappear so fast?

Solution 1:

Since this is a custom map, they probably didn't use the normal lava flow at all, but rather executed many setblock commands in a row to place flowing lava. Later, they place air again to remove it.

The syntax is:

/setblock <x> <y> <z> lava[level=<height>]

What you have to do is to plan out the sequence, get all the x, y and z coordinates and the lava heights for that spots and put it all into rows of command blocks that have a small delay between them.

That's really complicated. So if you don't need exactly the sequence shown in that video, but rather just fast-flowing lava, you can simply go into the Nether.
(Increasing randomTickSpeed no longer works.)