Whenever a spell from the Lore of the Serpent is successfully cast on a friendly unit, it gains +D6 to their Movement value and does not need to take any tests for Dangerous Terrain until the start of the caster's next magic phase.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
Whenever a spell from the Lore of the Serpent is successfully cast on a friendly unit, it gains +D6 to their Movement value and does not need to take any tests for Dangerous Terrain until the start of the caster's next magic phase.