Since Arcane Magic needs risks, but I don't feel the risks of 'spell fails, arm falls off' is fair, I'm going to reccomend various effects that can be the results of mana influxes.

LD:

Normal cast:

You gesture at a blue-belly crocodile.
The mana you were holding contributes to the spell.
A purplish, bruise-colored stream coalesces in the air next to your head, then explodes into fragments of mauve and violet that race toward a blue-belly crocodile!
The churning wave of colored light slams into its left arm, landing a very heavy hit!
The blue-belly crocodile is lightly stunned!
Roundtime: 1 second.

When the caster fails to properly position and form the stream of light.

1) The stream forms behind instead of next to your head.

You gesture at a blue-belly crocodile.
The mana you were holding contributes to the spell.
An influx of mana causes something to go terribly wrong!
A purplish, bruise-colored stream coalesces in the air behind your head, then explodes into fragments of mauve and violet!
The stream bashes you in the back of your head, causing you to black out!
You are unconcious!
Roundtime: 1 second.

2) The stream forms at an improper angle (tilted to the side) beside your head.

You gesture at a blue-belly crocodile.
The mana you were holding contributes to the spell.
An influx of mana causes something to go terribly wrong!
A purplish, bruise-colored stream coalesces in the air next to your head, then explodes into fragments of mauve and violet!
The stream clips the side of your ear, causing you to wince out in pain!
You are stunned!
Roundtime: 1 second.

3) The stream forms at an improper angle (tilted forward) beside your head. It lodges itself in the creature before exploding into nothingness, causing extra nervous damage.

You gesture at a blue-belly crocodile.
The mana you were holding contributes to the spell.
An influx of mana causes something to go terribly wrong!
A purplish, bruise-colored stream coalesces in the air next to your head, then explodes into fragments of mauve and violet that race toward a blue-belly crocodile!
The churning wave of colored light slams into its left arm, landing a very heavy hit! It drives itself violently through the left arm, shreading bone and sinew away! The sudden rush of magical energy entering the target causes it to shudder in pain!
The blue-belly crocodile is stunned!
Roundtime: 1 second.

4) The targetting stream does not fully form, causing the fragments to travel to various limbs instead of one focused area.

You gesture at a blue-belly crocodile.
The mana you were holding contributes to the spell.
An influx of mana causes something to go terribly wrong!
A purplish, bruise-colored stream coalesces in the air next to your head, then explodes into fragments of mauve and violet that race toward a blue-belly crocodile! The fragments
The churning wave of colored light slams into its left arm, landing a very heavy hit!
The churning wave of colored light slams into its right arm, landing a very heavy hit!
The churning wave of colored light slams into its left leg, landing a very heavy hit!
The blue-belly crocodile is stunned!
Roundtime: 1 second.