Template question.

[Yogibear41]

Have a question about a template. Say I have a Half-Fiend Wyvern. The creatures type would change from Dragon to Outsider, but in accordance with the template I would Not recalculate HD, BAB, Saves, but I would give it outsider skill points. Thus ending up with a 7d12 outsider.

Now comes my question. If said creature gained enough experience to be advanced via HD would the creature continue to gain Dragon HD(for 8d12 with +6 base saves at level 8) or would it begin to gain Outsider HD( and end up with 7d12+1d8 HD with +7 base save bonus)?

[Hackulator]

Have a question about a template. Say I have a Half-Fiend Wyvern. The creatures type would change from Dragon to Outsider, but in accordance with the template I would Not recalculate HD, BAB, Saves, but I would give it outsider skill points. Thus ending up with a 7d12 outsider.

Now comes my question. If said creature gained enough experience to be advanced via HD would the creature continue to gain Dragon HD(for 8d12 with +6 base saves at level 8) or would it begin to gain Outsider HD( and end up with 7d12+1d8 HD with +7 base save bonus)?

Creatures don't advance hit dice from experience. However, if you wanted to advance its hit dice, what you would do is advance the best monster and then reapply the template. This means it would end up with 8d12 HD.

[DrMotives]

Think about this. Your fiendish wyvern started off as a fiendish hatchlng at some point, yes? So continue to add HD under the same rules as you do for the un-upgraded version. Just remember the size changes, a wyvern becomes huge at it's first extra HD.