The function counts the number of even ASCII values in the input string and returns this count with an extra 'o' appended.

[CODE]:
```python
def f(x):
    count = 0
    for char in x:
        if ord(char) % 2 == 0:
            count += 1
    return str(count) + "o"
```
Let's do one more test to confirm our findings.

COMMAND: PYTHON(./temp/function.py "maze" "forest" "lake")