I got this by carrying my team, who were doing pretty poorly, just enough that we won with a single ticket remaining. Things to remember in Arena:
- Minion kills and God kills are both important, in my experience my teammates usually have tunnel vision and will chase god kills even if there are minions at your portal.
- Jungle camp buffs can really help. If you're a mage they stop you having to recall due to mana problems, if you're a damage dealer they make you deal more damage -- I have seen so many teammates completely ignore the jungle even at late game when you can kill a camp in under 10s.
- Don't chase. This should go without saying but unless you have some massive gap closer to use as an escape, don't chase. Unless their team is completely incompetent they will flock around the 100 hp fleeing ally and will punish you for trying to secure the kill with CC and probably your own death.
Specifically tips for the achievement:
- Try not to stomp the enemy team too badly. This is perhaps the hardest part of this achievement, usually games go one way of the other and the ticket difference is ~100. If your team is super ahead then don't wave clear and let the minions push to your base - your team is usually dense enough to only be focusing on kills.
- When the game is down to say 20 - 20, then end it as quickly as possible. A god kill is 5 tickets, minions are 1 (but don't count when a team has only 10 tickets remaining), as soon as you're in the required range go ham. It helps if you are super fed (minion gold makes a huge difference) and full build, Hunters can easily two/three shot non guardians late game in arena with proper builds.
- Play with friends. If you are playing with a full team of friends and you are winning you can easily manipulate the score towards the 20-20, then end the game. The key is to stomp early to get them to low-ish tickets then get your team to wait in base and let them hammer your tickets down with minions. When it's in the right range you'll have to obviously win, which may be difficult at that point since the other team have been gaining minion gold and yours haven't. Teamwork however can beat a team of randoms pretty easy, especially with a varied team comp, e.g. some CC, some burst, some AoE.
Hopefully this helped at least one person, if you downvote please comment on how this can be improved.