Improvement for level of the player:

Add level stat:
INSERT INTO stats(display_name, short_name) VALUES ('Level','lvl');

Replace the change you made to forest.php with:

$monster_exp = getMonsterStat('exp',$monsterID);
$smarty->assign('exp',$monster_exp);
$exp_rem = getStat('exp_rem',$userID);
$exp_rem -= $monster_exp;
$level = getStat('lvl',$userID);
$level2 = 0;
$exp = getStat('exp',$userID);
if($exp_rem<=0) {
$exp_rem = 100+$exp_rem;
$level +=1;
$level2 = 1;
setStat('lvl',$userID,$level);
}
$smarty->assign('level_up',$level2);
$smarty->assign('nlevel',$level);
setStat('exp',$userID,getStat('exp',$userID) + $monster_exp);
setStat('exp_rem',$userID,$exp_rem);

In register.php add this to the block of starting values of the player:
setStat('lvl',$userID,'1');

In index.php add those to the block of smarty assignments:
$smarty->assign('level',getStat('lvl',$userID));
$smarty->assign('experience',getStat('exp',$userID));
$smarty->assign('exp_remaining',getStat('exp_rem',$userID));

In index.tpl add those to the block of user stats:
<li>Current level: {$level}</li>
<li>Experience: {$experience}</li>
<li>Experience needed until level {$level+1}: {$exp_remaining}</li>

This is it

Improvement for level of the player:

Add level stat:
INSERT INTO stats(display_name, short_name) VALUES ('Level','lvl');

Replace the change you made to forest.php with:

$monster_exp = getMonsterStat('exp',$monsterID);
$smarty->assign('exp',$monster_exp);
$exp_rem = getStat('exp_rem',$userID);
$exp_rem -= $monster_exp;
$level = getStat('lvl',$userID);
$level2 = 0;
$exp = getStat('exp',$userID);
if($exp_rem<=0) {
$exp_rem = 100+$exp_rem;
$level +=1;
$level2 = 1;
setStat('lvl',$userID,$level);
}
$smarty->assign('level_up',$level2);
$smarty->assign('nlevel',$level);
setStat('exp',$userID,getStat('exp',$userID) + $monster_exp);
setStat('exp_rem',$userID,$exp_rem);

In register.php add this to the block of starting values of the player:
setStat('lvl',$userID,'1');

In index.php add those to the block of smarty assignments:
$smarty->assign('level',getStat('lvl',$userID));
$smarty->assign('experience',getStat('exp',$userID));
$smarty->assign('exp_remaining',getStat('exp_rem',$userID));

In index.tpl add those to the block of user stats:
<li>Current level: {$level}</li>
<li>Experience: {$experience}</li>
<li>Experience needed until level {$level+1}: {$exp_remaining}</li>

This is it