The status effect is easily seen by icicles crystallizing out of the affected target. While they are frozen, their turn is skipped until the ice thaw. It's exceptional that the debuff wears off immediately after skipping the target's turn, rather than at the end of the round, like other debuffs.
Passive abilities still affect their party while frozen, and abilities such as Pontifex Mortis' Resurrection will still activate if he dies while Frozen. While the Frozen status does not have a damage component, Water Heroes like IGOROK can use this opportunity to deal boosted damage with his Arctic Rush ability and with IGOROK passive ability Shattering Team. In addition, a CRIT with Selwyn the Enduring's Northern Gale or IGOROK's Polar Pounding will provide two turns of Frozen in conjunction with their Polar Master passive. Even though a turn is skipped, they skill gain energy for abilities.
Icebloom's Let it Snow will freeze the enemies, even if they dodge the attack, but they still have a chance to resist. High King Valkin's To War! (Artillery) can freeze the entire enemy team, never misses, and also deal massive damage.
The following heroes have or can inflict/apply Frozen:
Let it Snow (Special Attack): Ranged Water attack on all enemies with a chance to Freeze allies and enemies, allies are Frozen for 1 turn whereas enemies are Frozen for 2 turns. The Frozen Debuff cannot be Dodged.
Snowy Smash (Basic Attack): A Basic Melee Physical attack with a chance to Chill, Frostbite if target is Chilled, or Freeze if target is Frostbitten. Polar Pounding (Special Attack): Ranged Water attack on all enemies with a chance to Freeze.
Chaotic Bounce (Special Attack): Ranged Water attack on target enemy for [??% ATK] base damage with a ball, and then a number of additional attacks (bounces) on random enemies based on Bounce Attack trait. Enemy Heroes take damage and bonus damage based on total hits per Hero. Applies frozen to all enemies hit. If only 1 enemy Hero is alive, bounces will not occur. Frozen Laughter (Trait): Apply freeze to any enemy that attacks him twice in a row.
Icy Glare (Special Attack): Ranged Water attack on all enemies with a chance to Freeze or Stone each target. Purges all Venom on the targets for boosted damage. Serpent Strike (Special Attack): Melee Physical attack that steals all Buffs with a chance to Freeze. Purges all Venom on the target for boosted damage.