Realistically: like tempos should be grouped and large jumps should not be coming one track after another. If you absolutely need to mix, anyway.

I argue that if every single track in your programming is wildly different in tempo, trying to transition and mix them to begin with is not very smart. Let them play to fade out at the end of the file and start the next track from the intro. Bad, forced transitions sound a lot worse than no transition at all.

There are some interesting ways to do this: program your set in key, start the next track's drum intro during the sustain tail from the last note of the track, fade out in places where there are no percussion, and so forth. Trying to force an on-tempo beatmixed transition in these situations will just frustrate you and sound amateur.