The Regeneration spell will speed hit-point healing at the cost of mana regeneration. Mana regen is cut to 1/3, and hp regen is doubled. REGENERATION is a BIOCENTRIC Psionic Spell. It can only be cast on others if the Caster first masters the art of BIO EMPATHY.
At hero and below, this spell is obscenely useful for all characters (besides arcane and divine casters) to know. Please, learn it as soon as possible, and if you're a giant warrior, train your mana to cast it. It can make a HUGE difference for catching tics during a run. This spell is essential to all high hp/regen races such as giant, ogres, orcs, gargoyles, and especially trolls.
It's also worth pointing out that even with bioempathy you cannot cast this spell upon another player unless you are grouped with him or her.
See also Regeneration Gear.