The most common and most likely answer to this crossword clue is the 4 plus 6 letter word STEP LADDER
I've seen this crossword clue in The Times
S
T
E
P
L
A
D
D
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Buddy explains!

The straight part
We know that "Walk, run, climb using this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case walk, run, climb using this = step ladder.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
STEP LADDER noun- A ladder with steps or treads instead of rungs that is hinged in the middle to form an inverted V, with stays to keep the two halves at a fixed angle.
- The player over whom another player marks to take a spectacular mark.