Powershell is an external program, that has to be loaded each time it is used. So use it just once:
@echo off
cls
powershell write-host -fore Yellow -back Red "Merry" -NoNewLine; ^
write-host -fore Red -back Yellow "Christmas" -NoNewLine;^
write-host -fore Yellow -back Red "To" -NoNewLine;^
write-host -fore Red -back Yellow "Everyone" -NoNewLine;^
write-host -fore Yellow -back Red "In" -NoNewLine;^
write-host -fore Red -back Yellow "2020!" -NoNewLine
Powershell has to be loaded just once compared to 6 times before.
The ^ at the end of the lines is a "Line continuation", so actually, this is just one long (logical) line, splitted into several (physical) lines for readabilty:
powershell write-host -fore Yellow -back Red "Merry" -NoNewLine;write-host -fore Red -back Yellow "Christmas" -NoNewLine;write-host -fore Yellow -back Red "To" -NoNewLine;write-host -fore Red -back Yellow "Everyone" -NoNewLine;write-host -fore Yellow -back Red "In" -NoNewLine;write-host -fore Red -back Yellow "2020!" -NoNewLine
Note, cmd has a maximal line length (about ~8k chars), which limits this method.