(can you freeze a Regice)?
*Regice gets frozen in a block of ice*
Given enough Ice, it would actually be super-effective against fire, seeing as it turns to water when burned. But, because of that...
Flying Resistant to Ice (Can't bird fly over Glaciers?)
Don't birds usually need to fly south for the winter?
Bug Immune to Poison (They can usually create their own toxins, plus many bug types are poison and it would make sense with the below suggestion).
And the buggies that aren't producing their own poison?
Steel Immune to Grass (Can Leech seed drain life from a Magnezone/Registeel?
I'm going to continue campaigning for a simple resistance because I love watching those scenes where all the machinery - left alone for years - have been covered with vines and junk on the movies. It'd take awhile, but nature could eventually reclaim the cities.
Grass Resistant to Normal (What can a Jigglypuff/Stantler/Furret/Linoone do to a Forest except live in it?)
Other than get hit by vines, cut by razor leaves, leeched off by seeds, prick themselves on thorns...?
Water Immune to Fighting (Liquid, punching through water hurts your hands, not the water, lol).
You seem to be assuming water types are made out of water, rather than being fish with an affinity.
Fighting resistant to Grass (*chop through those vines)
Uh, try chopping through a few more things than vines. Ever bring down an oak with your bare hands? Kinda tough imagining that.
Lightening SE Vs Grass. (Thunder catches trees on fire).
Psst, lightning, not thunder does that. In that case, yes. But when you think about it, wood does not conduct electricity.
Steel weak to Electric. (Water is weak b/c water conducts electricity, same for metal).
Interesting note is that water turns back into its base gases when a strong current is run through it, while metal... doesn't.
Just felt like inserting an opinion there.