Luc.
Cards, many cards, have different ways of being dealt with. Permanents, generally, are removed by Explosines/Pullverizer. High-on-attack cards usually have not much HP and can be dealt with using a Maxwell or Otyugh. Cards with lots of cost are most preferably reversed, cards with useful abilities can be dealt with either by a Lob or a way described above, and such. Direct damage spells can be countered by a reflective shield, temponary dangerous situation can be countered with a Dimshield, and so on, and so on.
And the counters for Immaterial creatures are what Strategy Guide said. That they can't be countered with "creature control" is perfectly fine, as the creatures cannot gain positive effects, and are not very cost-effective.
Poison is even more broked than the immortals, as it stacks, it damages through each shield and Sundale, and the only thing you can do is excessive healing or Purify.