Radiant Half-Dragon

Hello All
    I was thinking about half-Dragons in wildspace and wondered what
special attack and special immunity a radiant dragon would have. The
breath weapon part was easy, but the Radiant Dragon has no immunity...
So with 3E should the Radiant Dragon have a immunity? Below is a small
conversion I will put on line soon to my site... holding back till I get
some feedback to see if anyone thinks the Radiant Dragon should have an
immunity.
    As for myself I was thinking that it might be interesting that a new
type of energy is created for spelljammer setting for monsters that live
and breath in space... cosmic energy? (i.e., radiation). The other
choice was immunity to 'force magic', like some feedback.

Radiant Half-Dragon Template 

Radiant Half-Dragon uses the Half-Dragon Template as given in Monster
Manual page 215 with the following addition to special attacks due to
them being a radiant dragon variety. Breath Weapon is three pulses of
magic missiles that each do 2d12, which the half dragon can assign into
separate targets. Half Radiant Dragons do not have any special immunity
as the dragon that sired them does not have such immunities.