User blog comment:Blizzardblade/Plant Tiers/@comment-24203813-20150926011721/@comment-24203813-20150926012820

I'm assuming it'll be like this:

S rank: Too dangerous.

A rank: Not too dangerous if you have the right plants.

B rank: Hard, but not too hard.

C rank: Can be difficult, but not a nuisance.

D rank: Can be hard in certain situations, but mostly harmless.

F rank: Not harmful in the slightest. Easy to beat.