Whenever I move up in tempo I try to line up the buildups so both songs would reach the drop at the same time. When the snare starts I start (people may hate this button but it would be extremely difficult to do this without it) to pitch the tracks up, with sync on to keep them at the same tempo as the speed up. I use filters, EQ, and effects on the slower track as it builds then bring it completely out on the drop. Works best when the faster track has space before the drop, like the Carnage remix of Spaceman for example.
When I move down in tempo I either use a reverb or delay effect with the freeze button, then bring in the other track with a filter on at a section without drums. Or I’ll line up the tracks so the breakdowns hit together and if the beginning of the breakdown for the new track isn’t very rhythmic you can use that to slow it down with out it being noticeable.
