Spellcasters are really easy to baby sit as they can usually do a few damage against most enemies which is all you need-- a few last hits after you plink a guy down to like 3 hp. Also most of the units that have low speed also have low magic resist so it's even easier.
Low strength physical attackers are the problem. Low defense spellcasters are slightly tougher to approach and there are less of them around. You could also swing at a myrmidon but good luck hitting. Doing 0 against the easy to hit knights sucks though. Course in Wendy's case her move range is also 4 which makes thing even worse.
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No problem!
This is a cute and pop genocide of love!