these are the 3 main changes that increased udyrs winrate
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towers became weaker. udyr is probably the singular champion in the game (next to nasus) that has a power relation to how strong towers are. udyrs power is directly related to the power of towers. make towers weaker, udyr gets stronger. udyrs winrate was kept in check in past seasons due to stronger towers. in fact the VERY strong towers last season with the tier2 shields and stuff like that did a real good job in keeping udyrs power in check
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having access to a realy strong jungle item that gives him alot of what he needs EARLY (compared to devour being later in the game). devourer is stronger than ludens on udyr for sure, but the powerspike from ludens is super strong much earlier runic echoes is basically just a ludens echo, but way cheaper. udyr is a champion that gets alot of benefit from ludens echo, probably the most benefit in the game, and you gave it to him for 1000 less gold
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the vision nerf. last seasons saw strong vision for both teams. vision that let you see where udyr is and move to counter him. now udyr gets to run around in a dark map without wards with teams having to "guess" in trying to counterplay him to know where he went with his hyper movespeed
also here is why udyr gets so strong ive done the math. and the jungle has alot more gold income than lanes. near 20% more. if you powerfarm the jungle you will have more gold than laners and be equal EXP
so the jungler really has the highest carry ability in the game if he powerfarms, due to having the most gold and having the power to pick where to move that gold on the map to pressure giving udyr a cheap ludens echo gave him more movespeed to move that max gold around the map to pressure the map
then once udyr moves that high gold around and gets kills with it, he then gets AHEAD of the game in gold and now is way stronger than everyone else
udyr in terms of 1v1 fights isnt that strong. compare to say, irelia or shyvana. irelia and shyvana have 4 damaging moves, udyr has 2 and a half.
take a irelia with botrk, rageblade, gunblade, maw, deadmans, and that will smack any 6 item udyr
the problem is udyr skyrockets ahead of everyone in gold
. After that i can power farm my butt off crazy fast and have 
done in the next 5 minute by simply just power my jungle and 9/10 the enemy jungle too. There's literally no drawback to counter jungling. You're free to face check their jungle, if they aren't there you can take their camps in the blink of an eye and get out. If they are there, most of the time you can just bully them out. If their team decides to collapse you pop bear stance and gtfo. Once 
