3 attacks will ensure he cannot cheese the other jungler's buffs with devour. This is the one thing stopping him from being an ok jungler. Let him be free.
Update: Riot has stated that they like his jungling right where it is now because it is in an ok state already. I'm so sorry everyone. I failed you. You trusted me, and I failed you.
KoKoboto37 votesVolibear can do the same thing with his smite + bite. Tahm Kench wouldn't even be that great at invading because he is really slow.
I don't know why they imposed this restriction on him, there are no good reasons.
SpaghettiVase1 votesHis ult into a bush would be effective if the enemy over extended
KoKoboto1 votesHis ult is unique and always works regardless of what position he is playing.
SpaghettiVase1 votesNot all the time. It's similar to a ryze ult where it's windows of power are very small and specific that you may not get optimal use out of it for possibly the entire game
KoKoboto4 votesAs long as it's off CD it always has a use. Getting to lane early or moving across the map are simple things but are still optimal.
Snowplosion1 votesVolibear can do the same thing with his smite + bite. Tahm Kench wouldn't even be that great at invading because he is really slow.
I don't know why they imposed this restriction on him, there are no good reasons.
Not really the same because Tahm could take off and run with the buff. Similar, but not the same.
NAY Wrecksauce7 votesTahm has reduced movement speed when he devoures enemy units... so wouldn't really call it running
SolarisCorvus9 votesTahm has reduced movement speed when devouring an enemy champion.
HeimerLmao8 votesThen use it on buffs too, what's the problem?
Troll for Trump2 votesNo, but Tahm can Q+W over the wall to flip off the opponent by resetting the buff.
TheSingularity33 votesHe cant qw over the wall because thats only one stack. He needs to have 2 stacks ready which would require him to be on the same side as buff. If he wanted a chance to steal it
Troll for Trump1 votesNo, he just applies 3 stacks while zoning the opponent off and then just resets the buff. He can go through the wall or through the bush, but being able to reset the blue/red buff is horrible for the enemy laner.
SoryInAdvance11 votesWhat are you talking about??
TheSingularity4 votesAgreed. He should elaborate
Troll for Trump1 votesHe attacks the buff 3 times, and either drags the buff to the bush with him, or it follows the opponent.
From there, he swallows it. QW if RIot allows it, or just straight up W. Because the "Patience" of the monster is already lowered enough as is from switching targets between Tahm and the jungler he's invading, when he swallows it, the buff will likely be reset with its Patience down to 0. If not, he spits it too far away from the spawn camp, and the buff resets.
I wrote enemy laner instead of enemy jungler*
DeadUnborn1 votesYeah but then tahm would be lsing xp, gold as well. He would have to pay and risk himslef to do that. Also blitz gets to do that more reliably and faster now
SoryInAdvance2 votesOkay but what the enemy jungle loses in the 5 seconds of tahm screwing around, tahm loses so much more and risks being killed. Your scenario really doesn't make sense as an argument against it.
Troll for Trump1 votesTrue, mb.
It can be used as counter-invades too
PapaGreg212 votesActually it is interesting because Voli would be in the same spot because he can't bite without building up frenzy with a couple of autos. But as you said, nobody has ever accused Voli of being a cheese counterjungler.
RiotZenonTheStoic28 votesThis would make his jungle crazy strong. He's an okay jungler right now, and we'd like to leave it there. If we make him a really powerful jungler, we would likely have to make some compensatory nerfs. This would leave him weaker than he is right now in top and support. We think he's best as a support, so that would be a bad thing.
Melledoneus16 votesHas there been any internal testing for this buff? Just wondering.
Elikain4 votesI think there was in the beginning. If this was the conclusion then, the same stands now.
DarkRitual5 votesHe's been nerfed considerably compared to his release state.
That said, I'm not convinced it would make him too strong. At least not with 
existing.
The Yetii Rider34 votesThis would make his jungle crazy strong. He's an okay jungler right now, and we'd like to leave it there. If we make him a really powerful jungler, we would likely have to make some compensatory nerfs. This would leave him weaker than he is right now in top and support. We think he's best as a support, so that would be a bad thing.
Not sure why the best method of balancing tanks in the jungle is making them take forever to clear it. Just not fun for the tank player.
RiotZenonTheStoic34 votes[{quoted}](name=The Yetii Rider,realm=NA,application-id=3ErqAdtq,discussion-id=AYUihrQy,comment-id=00120002,timestamp=2017-06-09T19:22:38.130+0000)
Not sure why the best method of balancing tanks in the jungle is making them take forever to clear it. Just not fun for the tank player.
There's a whole bunch of levers we have to balance tanks in the jungle. Clear speed is only one of them. OP is coming at this problem from a solution-first perspective though, without defining well what the goal is and what the intended change is. If your goal is just "make TK a better jg", there's a bunch of things you can do and it's not obvious to me why letting him devour buff monsters is the best way to execute on the goal. And like I said, whenever you consider changes to move toward a certain goal, you have to consider their unintended consequences. In this case, he's in a great place support, so any change that runs the risk of requiring nerfs after the fact harms a much more valuable state of things, namely that he's in a good place for his most played role.
Auz the Ripper31 voteshave you considered just letting his passive stack on monsters? it would only increase his clear speed a little and would let him use his stun to cut down on the damage he takes early.
Nebuul22 votesThis. Tahm is not a strong jungler anymore. He's not even OK. He just sucks in the jungle now. He was/is not an unhealthy kit for jungling, he just has some arbitrary weaknesses that are shutting it down.
The Yetii Rider9 votesThere's a whole bunch of levers we have to balance tanks in the jungle. Clear speed is only one of them. OP is coming at this problem from a solution-first perspective though, without defining well what the goal is and what the intended change is. If your goal is just "make TK a better jg", there's a bunch of things you can do and it's not obvious to me why letting him devour buff monsters is the best way to execute on the goal. And like I said, whenever you consider changes to move toward a certain goal, you have to consider their unintended consequences. In this case, he's in a great place support, so any change that runs the risk of requiring nerfs after the fact harms a much more valuable state of things, namely that he's in a good place for his most played role.
Clear speed IS a lever you choose to use, though. And all that does is force tank players to spend more time PVEing than other players and other roles. It's a BAD lever, because it sacrifices excitement and enjoyment playing the game for a menial repetitive chore.
SociopathFriend6 votesTechnically the issue is approached many ways, not only solution first.
An example of problem-first is mentioning the disparity between Syndra W and Kench W. The lack of equality between the two effects that are otherwise similar ability irks some players.
The Lexer9 votesBut, on the topic of taking buffs, why can Syndra still do it if TK can't? She's not even a jg!
AMYS GRAVE4 votesMaybe the goal is consistency in expectations. 
FantasySniper4 votesHe's an okay jungler right now
he's in a great place support
Jungler: Less than 45% win rate and 0.1% pick rate. Support: Less than 48% win rate and 3% pick rate.
That's not "okay". That's not "great".
DeadUnborn1 votesWhat if your goal is "making abilities that work consistently across characters". Blitz and Syndra get to pull buffs with no condition attached to them. Capping the max damage against epic monsters on Tahms W so that is fair while conditioning to have 3 stacks would be a good way to do this since he could not just steal a buff put of the blue. Mind you Blitz can already steal buffs from the support roll, and if you condition Tahm to have 3 stacks on buff before devour then he would be putting himself at risk just to be a little annoying to the enemy jungler, and deprive himself from his main source of damage while doing so
Chromatic Eagle2 votesThought he was intended as a top laner?
Chembaron Yamada15 votesIn early development, when he was still called "fish tank", they wanted to create a tank for the top lane. But that was before they determined his kit. Afterwards, it was pretty obvious that his devour would have huge potential in the support role.
That was when his intended primary role shifted from top to support. At least that's what I recall.
RiotZenonTheStoic19 votes[{quoted}](name=Chromatic Eagle,realm=NA,application-id=3ErqAdtq,discussion-id=AYUihrQy,comment-id=00120003,timestamp=2017-06-09T19:23:03.319+0000)
Thought he was intended as a top laner?
We pivoted half-way through development from top lane to support with a top secondary. When we allowed W to eat allies it just made a lot more sense to have him lane with an ally. So the intention is support first, top secondary, and that's pretty much what we're seeing.
XIII Vanitas1 votesSlightly OT, but can you please remove the ally-targeting prioritisation from his W? It feels horrible for TK players, because it heavily limits their agency. For example, if they try to devour an enemy champion really close to one of their allies, most of the times the game automatically targets the ally instead, but this could be counterproductive for them, so they're forced to refrain themselves from using the spell altogether.
THE RlVER KlNG21 votes"he's not a jungler so there's no reason for Riot to buff him"
Well considering he's a pretty shitty top laner and an extremely niche support, I'd be 100% down to shift him to the jungle. Jungle Tahm makes sense, and the jungle needs a strong tank jungler not named Zac anyways.
GelsominoKiller4 votesHe's not that bad in top.
He can be a quite effective counterpick, surprisingly.
Icestar11863 votesSame with Braum. Braum top can be surprisingly scary.
Neoaugustus16 votessame reason why syndra cant pick buffs up with a simple button... oh wait
ModAcademy Kayn2 votesAh yes, Syndra Jungle, my favorite position.
Gosh Darn3 votesHonestly I don't understand why he isn't allowed to be a jungler. He's slow as fuck and his biggest strengths were lost in the jungle, even before the nerf that made his ultimate passive not work on monsters. His Q and W poke along with his E shield + health return actually made him a pretty good laner. Jungling was never really an issue for his balancing.
So even before the nerfs his jungling wasn't an issue, but he lost his %own health damage on camps and the ability to damage buffs by spitting small monsters on them because he can't devourer the large monster.
Chembaron Yamada3 votesI don't think it is like they want to strictly forbid Tahm Kench to be a jungler. But he was designed to be a support and top laner.
So why should they put work into making a champion viable in a position he was never really intended for? Imagine everyone would do that. Boards would be flooded with request like "I want this change to make Jinx a viable top laner!" "We should work on this stuff so Udyr is able to go bot lane!"
A champion doesn't have to be viable in every position. You can play the champ in every position you want, but you can't expect Riot to make changes just so your champ becomes viable everywhere you want to play him.
SociopathFriend4 votesWell one of the major comparisons is how Syndra can pick the buffs up with her W, and unlike a lot of board comparisons, it does make some sense; there's no reason Syndra should be able to move a buff with W and Tahm shouldn't be able to do the same.
DuskDaUmbreon1 votesCorrect me if I'm wrong, but a monster grabbed by Syndra is still targetable, is it not?
There exists no such thing with Tahm.
GelsominoKiller10 votesBut we're not asking for the introduction of a new feature, we're asking for the removal of a limitation. "Tahm can't devour buffs" is an exception purposefully made by riot in order to keep the kench out of the jungle.
Eight Rocks2 votesWhat? That would be broken as hell. Kench already does massive damage to jungle creeps. Letting him Devour buffs would be stupid.
Visionova18 votes[{quoted}](name=Stardust Ray,realm=NA,application-id=3ErqAdtq,discussion-id=AYUihrQy,comment-id=0000,timestamp=2017-06-09T03:52:20.852+0000)
What? That would be broken as hell. Kench already does massive damage to jungle creeps. Letting him Devour buffs would be stupid.
Not really. His passive damage doesn't even apply to monsters (AFAIK it only works on champions).
That leaves him with only two damaging abilities, one of which is single target.
Blakiepug13 votes[{quoted}](name=Stardust Ray,realm=NA,application-id=3ErqAdtq,discussion-id=AYUihrQy,comment-id=0000,timestamp=2017-06-09T03:52:20.852+0000)
What? That would be broken as hell. Kench already does massive damage to jungle creeps. Letting him Devour buffs would be stupid.
Massive damage? Are we thinking of the same catfish?