Detonator I: Detonate a Flame Gem. Takes about 10 seconds if done fast enough. You can also use cascades to complete the challenge, but it's easier just to use a Flame Gem.

Spectrum I: Setup an L or T shape match using Red Gems, and make that and one normal match.

Coal Mine I: Simple. You can use a Flame or Lightning Gem for this challenge.

Chain Reaction I: Try to avoid cascades and vertical matches.

Gem Fall I: Just do whatever works for you. You want a median of under 30 seconds, that should be your target. My strat is to start at the bottom left and get 3 cascades.

Preserver I: Reset the board if you have a low amount of Green Gems. You'll need to start with 10+ and get good RNG if you want to go for the WR. You'll have to reset a lot here.

Firestorm I: Nothing special here. I like to detonate them all at once, but sometimes it isn't the best option.

Stratamax I: Flame Gems are quite helpful here, so are cascades. You want to complete it as fast as possible, while still playing well enough.

Arsenal I: Same strat as Firestorm, but you HAVE to detonate them all at once. It doesn't have to be at the bottom.

Bonanza I: The longest challenge. Creating Flame Gems and detonating them one by one is the easiest strat, but you can also use the Supernova strategy. Here's a video of the Flame strat in the eclipse challenge.

Survivor I: Make a Flame Gem somewhere near the Doom Gem, explode it and the Bomb Gem(s) on the board once you have under 19 moves needed, and make matchless twists as fast as possible. I'd holding down the space bar to make the twist to Detonate the bad gems, and move to the bottom left or right corners.

Voltage I: Make 5 Lightning Gems, and link them up for the grand finale of the run. (Side note, it takes less time for the Lightning Gems to link up if multiple Lightning Gems are on the same row or column, but sometimes it's not worth it to move them over.)

Enigma I: Stop the timer because the run's over already.