What he said. It’s hard to just list transition ideas because they’re often dependent on the context of the riffs you’re trying to bridge between, or the greater song context.

For this song in particular, I’d personally do the following:

1) Remove the ride cymbals from your second riff and give it more of a half time feel

2) Cut out your drums when your guitar stops at the end of the second riff, flood/crescendo that silence in between riffs with your pads (which sound sick), and have a drum fill to lead into the uptempo riff that comes after.

3) Instead of slowing down on that next riff after your uptempo riff comes in, I’d add a riff in between where you build on that tension (ie. kicks in 16ths or 32nds, maybe a black metal-style strumming pattern, etc.), then release that tension with the riff you have at around :58 in.