Hello!

Regarding the "speed" stat that you are talking about, it is called the "Initiative" in the game. In the arena, the only stat counted is Initiative and that is the one you have to boost or upgrade for you to attack first versus your opponent and this is by upgrading your Treasured Tools which you will have to set according to your ninja position or preference. The arena also gives a base stat of level 100 for all the players so everyone has the same stats and levels except the Initiative part. For the Daily Practice or Mission, you have to accomplish the missions (at least 2 Missions) that were given on the left side of your screen, accomplish 2 of it will give you the credit for the Daily Practice (for example, "Win a battle using 2 Earth Attribute Ninja")

Additional info, If your server is already beyond 50 days upon opening then your arena is already a cross-server which means, you may possibly end up being matched with a player who plays in older or newer server. That being said makes it clear that you are being paired with someone who has a Ninja of that kind. Hope my explanation gives you an idea about your inquiries. Thank you.