Here we go again.
There is a known bug where even though his health bar shows empty, he still has health left.
Yes, UDK is killable. There is a huge post made by HarleQuin showing how a fresh account, using only the starter champion can defeat UDK.
I realize that for the first few days you were steamrolling every arena match through "brute force". Sorry, that's over. You've graduated into having to build a team to counter other teams in the arena.
The daily quest to get a free energy refill only requires you to participate in 5 arena matches, not WIN 5.
A few pointers:
Kill the UDK first. His passive makes him stronger if you wait to kill him last.
Don't bring healing in your team. This includes passive healing, healing from gear (regen set), or direct healing if you want to fight UDK. This includes YOUR UDK. UDK vs UDK = 30 min fight and you still lose.
Don't go for bait teams with a solo UDK or UDK + 3 lvl ones. I know that team with 3 level ones looks juicy... it's not. That's some douche who takes joy in frustrating new players even when they are offline. Helpful players do not set up a 1 man defense using UDK.
Look at the opponentβs player level, not the team power. If your account is lvl 15 and theirs' is 65... 99% chance that UKD is in 6* gear and you will not beat him no matter what you do.
Use a Stun Set, sleep set, or destroy set.
If you have a heal reduction champion it helps.
Use Savage Gear on your nuker to bypass the ton of defense all UDKs are going to be built with.
If you're low level and see stone skin go up, exit the battle. You've already lost. Don't waste your time.
Use Ronda. Her entire kit is tailor made to kill UDKs.
Man... I thought all the UDK post would go away after Plarium gave away Ronda.