Special ability: Cold-blooded
Lizardmen receive a +1 bonus to speed and melee skill rolls when within 6" of a heat-source, and a -1 penalty to same when a heat-source is absent
This is perfect because the term "Heat-source" is abstract, therefore a lot of room is left for interpretation and as such, imagination.
"If someone ever tries to kill you, you try to kill them right back." -Malcolm Reynolds