One that looks like this.
Face it Paint is not capable of producing anything worthwhile. Paint serves no purpose whatsoever other than a feature to come with Windows - the ability to edit images and photographs. Sounds great. Trouble is it hasn't had anything done to it since Windows 95 except maybe the inclusion of formats other than BMP.
There is no point whatsoever in making a "mock" in Paint. It will be terrible to look at and will only ever result in flaming.
Get a copy of better software as listed in Mr Tom Servo's sticky thread. If you can't *obtain* this software, don't mock. Simple as.