##Perl, 148 bytes

146 bytes of code + -pl flags.

$_=O x($x=$_+1);s/O\K./_/g;for$i(1..($y=<>)){$b.=($i%2?$_:_.s/.$//r).$/}}print$_="\e[H$b";while(/O/){$r=0|rand$y*$x+3;s/.{$r}\KO/X/s||redo;sleep 1

To run it:

perl -ple '$_=O x($x=$_+1);s/O\K./_/g;for$i(1..($y=<>)){$b.=($i%2?$_:_.s/.$//r).$/}}print$_="\e[H$b";while(/O/){$r=0|rand$y*$x+3;s/.{$r}\KO/X/s||redo;sleep 1' <<< "6
4"

Perl, 148 bytes

146 bytes of code + -pl flags.

$_=O x($x=$_+1);s/O\K./_/g;for$i(1..($y=<>)){$b.=($i%2?$_:_.s/.$//r).$/}}print$_="\e[H$b";while(/O/){$r=0|rand$y*$x+3;s/.{$r}\KO/X/s||redo;sleep 1

To run it:

perl -ple '$_=O x($x=$_+1);s/O\K./_/g;for$i(1..($y=<>)){$b.=($i%2?$_:_.s/.$//r).$/}}print$_="\e[H$b";while(/O/){$r=0|rand$y*$x+3;s/.{$r}\KO/X/s||redo;sleep 1' <<< "6
4"