The Arena is essentially a boss rush mode, pitting you against both mini and regular bosses in a row with a hub world in - between that gives you a breather and
limited health regeneration.
Not exact matches
These gameplay alterations range from completing certain sections in a given time
limit, to facing more powerful enemies, losing
health regeneration capabilities, and more.
Without
health regeneration and
limited options for attack (shotguns or melee only), your best chance of survival is to move around the map as a pack with your squad mates.
If you do take some damage, you will need to heal yourself using bandages or med kits since there is
limited auto
regeneration of
health, which will refill parts of 1 bar of the 5 of the
health bar.