You can also avoid the 'sliding' problem of skipping over elements because you removed the element before them by iterating backwards:

for(reverse (0 .. $#items)) {
    splice(@items, $_, 1) if ($items[$_] == 1 || $items[$_] == 3);
}
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Which is slightly obfuscated, but works because the sliding end of the array contains only the elements you have already checked...