In my T20 campaign (currently taking place on a post-apocalyptic world where the players are marooned) I've been pulling out the occasional DnD Monster Manual beast as a "mutant" creature to put against the PC's.
Be aware, if you chose to do this that the Challenge Ratings of the creatures are not very accurate for determining the challenge of the beast in the T20 rules. Mainly due to Armor Class (Armor Rating), Lifeblood, and the damage ratings of monsters.
For example, there was a CR9 creature I put against the part last week. Bite damage was 2d8+8. Now, in DnD vs. 9th level characters that's painful but not super deadly. In Lifeblood vs. PC armor factor? That +8 on the damage roll is DEADLY. Super super deadly.
Just an fyi from my recent experience.
Be aware, if you chose to do this that the Challenge Ratings of the creatures are not very accurate for determining the challenge of the beast in the T20 rules. Mainly due to Armor Class (Armor Rating), Lifeblood, and the damage ratings of monsters.
For example, there was a CR9 creature I put against the part last week. Bite damage was 2d8+8. Now, in DnD vs. 9th level characters that's painful but not super deadly. In Lifeblood vs. PC armor factor? That +8 on the damage roll is DEADLY. Super super deadly.
Just an fyi from my recent experience.