Replay Mod Forums

Can we use replaymod in monetized youtube videos and thumbnails etc on youtube?

The ReplayMod is provided under the terms of the GNU General Public License Version 3 or (at your option) any later version. See here for the full license text.

So for your particular question the answer is: yes, you may use content created with the ReplayMod in whatever way you like (that does not apply to the mod itself, see the license text for that), provided you follow the conditions of the source material (you recorded the replay yourself or have permission of the person who recorded it; and the Minecraft Terms and Conditions; plus any resource packs or other mods you use, etc.).
However, we do ask you to provide a link back to the ReplayMod.com website in the description of any video/content created with the mod, so that others know how it was produced and can use of the mod themselves.