This tutorial will show you how to place your custom creatures, or bonus creatures, into the mission editor, so you can have them wandering around maps.
1. First of all, you need to find where you've saved your custom/bonus creatures. They will be in the form of 2 files: an .EBP and an .SGM.
2. Second, locate your RDN tools installation. It will normally be: c:\program files\relic\impossible creatures rdn tools
3. Now, in your RDN tools directory, open it up and find the Data\Art\EBPs\Stock folder.
4. Copy the .EBP and .SGM file from where you found them in step 1 into the folder you located in step 3.
5. Load up the mission editor, and now in your creatures list you'll see the custom/bonus creature.
Hope this helps