Each one has 6 nails in addition to the one nailed into the wood. The challenge doesn't say anything about not using a seventh nail that does touch the wood.
Assuming Batman is another PC, it could be that player overestimating. And also being as uncreative af because Batman's backstory is a standard part of the Junior Edgelord Unhappy Meal character design package.
Rules nerd nitpickery: If this is for D&D, scaling spells to caster level is a Third Edition mechanic and was done away with for 5e due to balance issues with the new system. Also that's clearly a conjuration spell; abjuration is protective or purification type magic.
Not that this really matters for a "summon giant salad" spell but OCD demands and such.
As a tall person I can confirm that using a short girlfriend's head as an elbow rest is a gesture of affection. I also do this with platonic friends, to mixed results. My favorite recollection is walking up to a college friend on campus who was talking to someone else, she introduced me and I did the armrest thing while joining the conversation. After a minute the other person said "Um, are you gonna..." And my friend said "Nah, he'll get bored with it eventually and I'm used to it. I have a lot of tall friends."
The only thing that little fence will accomplish is guaranteeing that when the inevitable cat to tree contact occurs it will be at speed and above the tree's center of gravity. Those furballs can jump.
How about we discuss those heros in the foreground? Conan-core "armor is for wimps" beefcake/cheesecake aesthetic featuring brown hiphugger jeans, and all illustrated by someone who has no clue how to world a real weapon. Also wtf is the woman even posing with (because I am not going to suggest she's"wielding "it)? Maybe it's a staff and her ridiculous pose can be attributed to somatic casting, at which point maybe the one in the middle is a bard doing a stripper sword dance with that terrible stance. Left dude still needs to choke up with his right hand if he wants any kind of power on his swing.
The example in the op says nothing about whether it was ever possible to diffuse the bombs in the first place, so it's unclear if there is any element of agency at all, let alone how difficult the scenario is to win if that's even feasible.
I have a mixed collection of plastic, metal, and fancy metal dice plus a one pound metal Zocchihedron. I make no excuses. As long as you're willing and able to carry them around to a game you cannot have too many dice, especially they're cool ones.
The metal ones are the best. They're extra shiny, they make more satisfying sounds when rolled, and in emergencies are more effective as weapons (both as caltrops and projectiles).
You want mental damage? I just got my first dose of rural Florida about an hour ago. I didn't get out of the car but it kinda felt like I was driving through a haunted forest on an alien world.
Each one has 6 nails in addition to the one nailed into the wood. The challenge doesn't say anything about not using a seventh nail that does touch the wood.