I suppose there's not much startegy to Rusty, given that her bleed and conversion effect incentivize going all in on the opponent, which for the most part works against heavy defenders such as Armed Forces, Resonant Evil and Surgeon General (which kinda surprises me that immunity can also be converted). But the percentage of conversion is fairly low, so if anything multi-hit Blockbusters and SMs are the most ideal solution, (i.e. Violet Grudge, Cruel Lily, Death Crawl, Buer Thresher and Buer Overdrive).
However that's naturally a risky strategy with some of the defenders stated earlier, and perhaps another downside would be the fact that she's a natural bronze, which in turn means her stats won't be as strong as something like Buzzkill. That doesn't stop people from carrying her to diamond, and I can totally see why; who knows, perhaps she's my next light type to diamond.
As for marquee ability, I guess it's only natural for her to have Grudge, given her weaker stats. I do prefer Tainted Blood in general myself, given that it saved a few of my battles, something Grudge could not have done, however, I am willing to make exceptions when it fits, which is exactly what I did with Rusty.
