How is a bomb champ built for live arena?

If you have the gear, pinpoint is best since it offers protection against polymorph. Feral & Stoneskin are arguably next best.....I don't use any of those gearsets because all my bombers have been geared for a long time.   

As for the stats, you prioritize speed, accuracy & attack, and would ideally pair them with a toon that can give them acc/atk buffs like Arbais or Yoshi.  

If you are gearing Shazar, you also want 100% CR so he can drop the bomb timers. Same with Astralith so she can do the A1 TM Boost.  For other bombers, some peeps would tell you to sacrifice CR for more Atk, but I build with CR anyway.

Gearing footnote for Astralith only: she really really wants Swift Parry due to the synergy with her passive.