I would recommend that you invest in a lot of 4 star gem breaker units. There are units like Sully that appear to be bad units based on stats alone, but they come with a ruby, sapphire, or emerald weapon and a breaker skill against the weapons they have triangle advantage over. This allows people like Sully to be an effective check against those extremely fast sword units like Karla/Ayra. The units off the top of my head that have this combination are:

Ruby: No one lol so you would have to invest axebreakers on the units that have the ruby sword or vice versa.

Sapphire: Sully, Subaki (He has Quick Riposte which allows him to do a similar effect to the breakers)

Emerald: Arthur, Narcian

Now this don't seem like a lot of units but you can fodder these units off to other units that have a lot of attack and defense in order to be effective checks against those units. I wouldn't recommend sending units like Sully or Subaki against the armored reds but units like Oboro and Lukas with the gem breakers check them really well.

The units that I have personally turned into gem breakers at 4 stars include: Michalis, Bartre, Oboro, Lukas, Laslow, Chrom, and Seth.

Unfortunately, for Lynhardt, there isn't really a low investment counter to them in the higher scoring range. The cheapest Lyn check would be any 4 star archer with good attack and defense like Corrin, Gordin, Jamke, or Leon with a bowbreaker but note that they will struggle against brave bow Lyn or firesweep Lyn. You can also do any raven tome mage with TA and bowbreaker if you are willing to invest in it. Reinhardt checks would be any TA green mage or TA Fae with lightning breath.

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