Some metallicas have this effect:

You may untap this creature and change the target of your opponent's creature to this creature or one of your tapped creatures.

It applies when i attack players right? Such as when i use a creature to attack, he can use a tapped metallica and an untapped creature as some sort of semi blocker? In other words, it's not limited to attacking creatures right and i can use them as blockers?

I may refer to the effect of this guy, to see if we understand this effect correctly: http://duelmasters.wikia.com/wiki/Phantasm,_Moon%27s_Radiance
I think, as on this creature it seems to be vice versa: "When one of your opponent's creatures attacks, you may untap this creature to change the attack to one of your tapped creatures."
So this is actually just a redirected battle you can use once because you can only untap 'Phantasm' once.
But maybe there are some other example that stick to your explenation, however there may be metallica cards that just tap one, so you could basically use it again and again.
It helps if you could link an example for such a creature here.

OcaVan wrote:I may refer to the effect of this guy, to see if we understand this effect correctly: http://duelmasters.wikia.com/wiki/Phantasm,_Moon%27s_Radiance
I think, as on this creature it seems to be vice versa: "When one of your opponent's creatures attacks, you may untap this creature to change the attack to one of your tapped creatures."
So this is actually just a redirected battle you can use once because you can only untap 'Phantasm' once.
But maybe there are some other example that stick to your explenation, however there may be metallica cards that just tap one, so you could basically use it again and again.
It helps if you could link an example for such a creature here.

I was saying that can i use that ability when opp's creatures attack me as if it was a blocker, or it is just a shoddy guardman ripoff.

That ability can be activated when the opposing player attacks the player controlling a tapped Phantasm (or another creature having similar ability) to redirect opponent's attack (either to player himself or one of the creatures) to one of the controlling player's tapped creatures. So in that sense, it's very different to blocking. Your creatures have to be tapped.

"it's very different to blocking. Your creatures have to be tapped."

This is true. Its actually referred to as Reverse Blocker (like the Reverse Fury Charge on jokers).

However, after looking at Phantasm again, and basing it off clearer wording from these new creatures, I'm updating his text of...

When one of your opponent's [[creature]]s [[attack]]s, you may [[untap]] this [[creature]] to change the [[attack]] to one of your [[tap]]ped [[creature]]s.

to

You may untap this creature to change your opponent's creatures attack to one of your tapped creatures.

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Unlike http://duelmasters.wikia.com/wiki/Faywon,_Green_Silver and http://duelmasters.wikia.com/wiki/Morgen,_Blue_Guardian he doesn't actually have "to this creature" part.

Yami_Michael wrote:You may untap this creature to change your opponent's creatures attack to one of your tapped creatures.

This is indeed now much more straightforward and clear. The ability is an interesting one.