Lord Ifrith is a powerful Fire Demon purchasable from the onyx market as a permanent troop. He is one of the most expensive items available for good reasons.
In terms of power, his damage is unmatched except by fully upgraded Fire Demons with Ifrith's Blessing Kami Tree upgrades. His health is between a level 3 and 4 Fire Demon and does twice the damage of a level 3 Fire Demon.
Unlike other Fire Demons, Ifrith does not gain additional bonuses from the Kami Tree because he is a unique troop, not a generic bonus troop. He also rarely explodes when killed, though it can happen from time to time. Perhaps most importantly, he cannot be frozen and does not take extra damage from being frozen.
Lord Ifrith's Pit is available for purchase for a whopping 14800 onyx and lets you deploy him only on attack. Despite looking like a 5x5 camp, it is actually only 3x3.
Upgrading to Prince Ifrith requires a token that costs 10500 onyx which allows the upgrade to level 2 for 1 essence.