If X is resistant to Y then Y is what against X?

In pokémon there are 18 elemental types which have various strengths and weaknesses. For example, consider the following three statements.

1. Steel is immune to poison.
2. Steel is resistant to ice .
3. Steel is weak to fire.

Thus "weaknesses", "resistances" and "immunities" are plural nouns used to describe the defensiveness of an elemental type. On the other hand, consider the following three statements:

1. Fire is strong against steel.
2. Ice is ??? against steel.
3. Poison is ??? against steel.

Thus "strengths" is a plural noun used to describe the offensiveness of an elemental type. However, I need two more adjectives to replace the question marks in the aforementioned sentences.

For the opposite of "resistant" I thought of using "weak". For example, "Ice is weak against steel". However, the plural noun "weaknesses" is already used to describe the defensiveness of an elemental type.

For the opposite of "immune" I thought of using "ineffective". For example, "Poison is ineffective against steel". However, the noun "ineffectiveness" doesn't have a plural. Can you think of single word adjectives and plural nouns for these two cases?

Solution 1:

Ineffective and Useless respectively.

From M-W:

Ineffective: not capable of performing efficiently

Useless: having or being of no use

As in:

Fire is strong against steel.

Ice is ineffective against steel.

Poison is useless against steel.