Bio ball: identify a bio ball with a clumps of MMM with the mobility of drop ship tech. this army is really strong in destroying structure with stim marauders can finish a nexus in split of a second.
What is hard when you vs a bio ball army? well Bio ball so far is the hardest type i have encountered. basicly depends on how far into the game you are. a good T will never 1v1 face to face with you using a bio ball, they will split them in 2, 3, even 4 small squad and drop them at different places, stim and take out all of your key structures and safely load away. Annoying, strong, low cost and easy to reinforce.
So what should be you tech choice vs Bio ball? storm is a MUST. why? bc the ability of dropping everywhere require you to have the mobility to counter and wraping templars with storm is the only solution. Lots of people have never notice but the heart of bio balls actually rely on the energy in the medivac. always try to finish the medivac after the units die. stacking medicvac will simply create a night mare for your army to make a counter push. Lots of T feel the bio ball is so weak vs storm so they mostly get marauder so most P got a wrong idea that they would be safe if they play air tech. This is really wrong due to the fact that T starport should have reactor for medivac and now they can produce viking. another thing is that air tech cant deal damage "Fast" enough to finish a large bio ball b4 the dealt their damage and run away.
careful vs ghost
for more info on bio ball, watch craft cup game 3 yesterday :D
2nd composition: units mix with sieg tanks. Death wall it is huh? =) Seig tanks with smart AI is the nightmare to 1 group control players. the pathing of sc2 make everything clumps together so good for tanks to splash. mid game the army should be tanks rines raven in transition into late game tanks hellion vikings.
Its actually really easy to counter this type of army if you actualy know what you are doing. they Key thing is ob. has obs watching his army to know the sieg and un seig timing in order to attack. since storm wont help you much, always consider taking the dark shrine insteal of TA. why? the biggest reason for a death wall to exist is for the T to freely expan and 1 DTs can put a stop to that. consider the immobility tanks army is, Toss has so many option to harras T's main: wrap prism, VRs, DTs blah blah.
always use colossi if you have not choose the stormy road. the range on colossi will safely burn tanks away 1 by 1 if you can wisely choose a good engage angle for yourself. tanks should be able to shoot you as you shoot them but remember, they hv no vision of you but you hv vision from the obs. immortal is not bad of a tanks counter except the immobility of it when T try to abuse cliff. a good immortal wrap prism micro BW style should solve everything but wrap prism is really weak so this require some practice skills. I wont suprise to see that in near future though: wrap prism immo drop micro counter tanks by whitera + HuK =)....
air countering tanks is just unfair but always consider what air tech to get wisely. they are expensive and take time to get so dont over do it or else blizz will turn our VR into the new Scout :<....
hold on, did i forgot to mention chargelots vs tanks? oh well, if you still dont know about it after almost 12 years of BW, you deserve a lose ...
lasty: air tech of T aka "holy mother mercy", the BCs fleet.
1st of all, i would like to include thor into this category. the reason mostly bc thor and BCs has similar characteristic such as "large model" for better repair, can deal great amount of damage using 1 spell, immobility and contain unused energy most of the time.
Best count to "the fleet" would be carrier with mother ship while DTs are sniping the enemy supply depos. he will need scans for both your main army and DTs + he cant move his army back consider how slow BCs are. always has few templars to feed back since yamato are just scary. Mix in stalkers if you needed but stack them up and go all at once, target fire instead of A move on the ground. Personally i have no Fun when i see a T pull scvs and put on auto repair. i have lost a game when a guy went thor marines rush with scvs repair, it just brutal, the guy was not even good.... but yeah, care if he is repairing. Might wana try to step back to kite him to move up but the best solution is to send a small group blocking his reinforce and kill scvs in his base while he is pushing.
oh yeah, i mention harrasing T when they pushing alot didnt I? always consider on "how much forces you have. supply depo and scvs might be worthed but the later the game, the better it is to try to take out the production building. taking about barracks, factory will put their macro into HELL! supply can be call down but i know for sure, barracks and starport cant be =)