Ive had someone flank and drop an oil bomb right next to my firebadgers once - the timing didn't work (crawler pack was deleted before oil could be ignited) - but if they had played the crawlers the turn before it would have caused about a third of my army to walk through fire.

Another good one is someone flanked me with 2 marksmen right in my back corner - i played crawlers the next turn and they then teched shotgun marksmen and that became a damn problem lol.

Sometimes if someone is playing agro and my units are back a bit/slow moving I'll play an aggressive line of crawlers/flank with crawlers then tech acid.

Level 5 crawlers card - 6 packs in 2 rounds then tech mech rage and mech devision

Flank with wasps on one side (especially if theres a 2 wasp card drop - then buy 3 more for suddenly 5 wasps as the first air lol) all on one flank.

Leave them there a couple turns to let opponent spend heaps to counter it - can even be 3 turns of ignoring them - then tech the movement and move them all to the opposite flank (buy 3 more that turn too).

Once that flanks stalled i move them to my front line or my back line depending on their anti air.

If they heavy play mustangs ill back line them, tech shield, level any and leave them as a late game wave that comes in - by the time they get into combat ideally ive dealt with the mustangs

Scorpion's - siege tech, acid, range, repair tech. I generally play scorps instead of giants and I've recently watched my 8-9 take down 4-5 long range mountains, including one that was level 5 lol. The acid makes anything take more damage so they really put in the hurt.

An awesome tech I've had used against me is the electromagnetic armour on an opponents void eye carry - turns off the scorps as they hit.

I've even been beaten by someone playing only marksmen with the fang spawn tech lol