I stand corrected. It seems Timber kills between 65% - 85% depending on the character weight. But I still don't think it's really overpowered and here's why.
- Comparison with Little Mac's 1-hit-KO
Disadvantages: Unlike Timber, this moves will kill you as soon as 10% (estimate) even on heavyweights, it's unblockable, it comes really fast (which makes it hard to react to) and can be combo'd with d-tilt on low percentages.
Advantages: Little Mac's 1-hit-KO needs the bar to fill up per us, whether you hit the target or not. Though Timber has something similar going since the tree will die after a couple of seconds and you'll need to plant another one.
- Comparison with Mr. Game & Watch's Judgement
Disadvantages: Judgement Lv.9 is a 1-hit-KO guaranteed as far as I know (though heavyweights might survive it at 0% and with perfect DI). Judgement can be combo'd with down throw at mid-percentages and it comes really fast.
Advantages: Judgement is completely random so a Lv9 isn't guaranteed.
- Comparison with Jigglypuff's Rest
Disadvantages: Jigglypuff's Rest kills around the same percentages as Timber (if not earlier). Rest keeps damaging the opponent even if they don't kill it.
Advantages: Rest sends upwards and Jiggs stays asleep for a while which makes it easy to punish if missed or if the opponent survives/respawns fast.
The previous comparison are taken from the Timber perspective, meaning that it is "Disadvantages towards..." and "Advantages toward..." Also, I'm talking as if it were in a competitive stage.
- So, why do I think the One-Chop Trick isn't overpowered?
While Timber is a strong move, it still needs to be planted and watered before you can cut it down, which makes this move pretty situational. In other words, it's hard to force the enemy into the move's range.
The attack itself also isn't as fast as one would like and relies completely on the element of surprise. The attack is by no means slow, but it still gives enough time for people to react and block, evade, or whatever. You mentioned that people usually expect it to be a double chop attack, but that's because the trick isn't widely known. Once people learn more about it it'll become more known and people will start expecting the One-Chop Trick.
In theory it sounds like an overpowered ledge attack. It's like the Bowling Ball but with more range! But you still need to take in the fact that if you don't have it plant it or watered, you'll have to perform them before being able to cut the tree. The opponent will realize you're trying to edge guard him and recover fast or high.
I'm not saying the move is bad, just not overpowered. I also want to take this time to say that I don't consider the other moves I talked about overpowered either.
1. Timber doesn't kill as early as KO Punch, but KO punch needs to charge up, and is lost by being attacked. One could say that for the tree, but believe me, if Little Mac could recharge his KO meter every time he had a few seconds to himself, KO Punch would be a lot better. Also KO Punch doesnt act as a shield from projectiles, and Timber has a MASSIVE hitbox, and even deceptive to some degree.
2. Comparing timber to 9-hammer is like comparing Pikachu's down B and Bowser's fsmash. They're both used in completely different situations. And I'd rather bait my opponent into my attack, rather than do a combo that has a 1/9 chance of working. Also it's not a 0% kill, but its close to it. Still, timber can kill at a VERY early percent regardless.
3. Rest leaves Jiggly WIDE open. After a death by timber, your opponent can't punish you. After a rest respawn, unless you're lucky enough to get a star KO, your opponent WILL punish you. In fact, if Rest idoesnt kill, due to perfect DI + scraping living percentages, your opponent can also come down and punish you.
And I realize you touched on these points, but I feel you aren't giving timber enough credit where its due, despite knowing these points. It can't be compared to those three moves, because it stands out on its own, even alongside these moves.
Now about the whole planting thing:
1. You can sprinkle the sapling with water, without making the tree grow. This will make it so that next time you water it, tree will sprout IMMEDIATELY. Tree also stays out for 30 seconds, giving ample cutting time.
2. Let people know about the one-chop, who cares? That just means they will have to be more wary about which way they approach when we plant the tree.
Is this the best thing ever? No.
Does it stand along side the 9s, the KO Punches, and the Rests? I'd say, most definitely.