Mission 20 was a bit bizarre. Black Hole had five Black Crystals (that heal all units around them by 2 each move), but started with a load of assorted units on just 1 point. Of course, each turn they were repaired, so obviously a balance was stuck between blowing up dangerous-when-healthy units before they were repaired, and destroying the crystals to stop units being repaired. Wiped out most of the dangerous units before they really started fighting back, but was sloppy and lost many of my units in the process.
Luckily, there was a factory and an airport on the map, so I took them over and soon Neotanks and Stealth Bombers were on the attack and the final Crystal fell. Hurrah!
Mission 21, on the other hand, is a bit harder. Well, a lot harder. Not only is it against the clock, but Black Hole have loads of powerful units to start, and a giant Black Cannon which can fire at any unit in 1/3 of the map. I do have three teams, however, but they start off weak and there’s a rush to get to nine missile silos to destroy a satellite, which detracts from the fighting somewhat. Anyway, I died. Bah.