So I've registered specifically to leave some tips to other players on how to beat Mastery 25 with all characters.
Archer is currently the weakest class even though before the last patch it was the strongest one. Usually the archer dies on day 3 (and sometimes even day 1) if you're unlucky with talents. Your best bet is to get an early piercing. Second best is, surprisingly, the ring talent which apps all stats. Third best is double strike. After getting any of those and some damage/attach speed talents you should be fine.
Wizard is broken with the right talents. Currently orb build is the best. If you manage to get blazing orbs early, the explosions will carry you through the first half of the game, and later you'll become invincible.
Warrior is well-rounded and doesn't need any specific talents as its attack is a huge splash. Just focus on attack damage and attack speed.
Summoner was the weakest previously, but now it's pretty okay. Still needs the right talents to survive. Early on you need to find either +50% HP for summons or spectral summons. Then you need the talent which gives +10% summon speed on every lifesteal and get lifesteal as high as possible.