Area of Effect: The radius of the explosion caused by collision (with either an enemy or a terrain obstruction) is affected by all AoE increases, with a base radius of 9. Full spell damage is done to any enemy in range of the explosion. Damage dealt to the initial target that caused the explosion is also affected by AoE damage increases and reductions, however the intial target won't take double damage from the hit and the explosion.

Pierce, Chain, Fork: Enemies hit by a projectile that pierces, chains, or forks will take full damage from the hit, but the projectile will not explode until it hits an enemy and does not pierce, chain, or fork, or hits a wall. This means that the damage dealt to pierced enemies won't benefit from AoE damage increases.

Shotgunning: Each enemy can only be hit directly by one projectile per cast. However, if an enemy is in range of the explosion effect of more than one projectile from the same cast, and those projectiles each exploded on different enemies or a wall, it will take full damage from each explosion.