Board Thread:Questions and Answers/@comment-46154384-20200707063319/@comment-29914576-20200707100857

There appears to be two long standing possible comboes, but each of them require really good RNG and force grinding.

1) Grand Sabotage + Apache Prime: You are forced into Razor Rotors + 210 Ninja until Dartship is bought, so you will require insane distraction RNG on Round 47, if not you will fail on other rounds. Wouldn't be surprised if the community as a whole has spent over a hundred hours attempting to get the RNG. Free if 47 is ever passed.

2) Master Bomber + Tsar Bomba: Round 79 is extremely difficult and has only been executed ever by two players, and likely requires insane micro/RNG. Passing Round 79 also does not mean this is free, since rounds after still have problems and will require good micro.

I believe there may be a few other 2TCs that simply require insanely good timing or something else, but it's good to note that 2TC is milked dry very quickly due to it being such a prestigious challenge (even if comboes are free simply due to balance changes). So, overall it is difficult to find a combo that simply isn't physically impossible or just don't work due to weaker towers.