These are normal farming levels. Very easy. I don't think tips are really necessary just play the level normally and wait for an elemental. Though my tip about avoiding attacks like Earthquake still applies.
Same goes for Growth and secret Growth.
If you have a more specific question I would be happy to answer but I can't imagine what problem you could be having on those levels.
Thought of a Pichu tip! Pichu can't win the level for some reason so you don't actually need to defend. This makes grinding much faster and easier. The tiny amount of XP they give isn't worth the time spent sending your Pokemon out.
18.104.22.168 wrote: I can see a special strat being needed for Truth due to the Boss Bulbasaur...
Not really. It's tedious to move your pokemon from the Bulbasaur to the main play area but I don't think there is any strategy to help with that besides having a lot of firepower. If you are high leveled you could let 1 or 2 Pokemon fight Bulbasaur and the rest to defend to save a bit of time.