Lion is pretty easy to beat, despite the number of big creatures.  There are 5 rooms where creatures that, once destroyed, never come back.  Two of those rooms have Manhandlas, the other three are Blue Gohmas.  You must beat at least 1 Blue Gohma and 1 Manhandla if you want to clear this dungeon.  The rest of the labyrinth has Pols Voice and Blue Darknuts, along with Zols and Gilbdos.

When you enter the labyrinth, you got two options.  If you don't have the Magic Wand, don't worry about this next step.  But if you already had the Magic Wand, go left from the front room and take out the Manhandla via bombs (always the best way to take care of Manhandla due to the fact a single bomb can kill the whole thing if timed right).  You may also ignore it if you are low on bombs.  Now go left from that room again and take out all the enemies (blue darknuts).  When that is done, open up the passageway for the Book of Magic.  Now your magic wand is a combination Wizzrobe/Red Candle weapon.

Now return to the front room of the labyrinth.  Plant a bomb in the north wall for another door.  Go north through that door and take out another Manhandla.  This one must be killed in order for the shutterdoors to open.  Keep going north, bombing out northern walls if possible, while trying to kill or avoid the Darknuts.  Once you reach a room where the first blue Gohma is located, give him two arrows to the eye.  Now the shutterdoors will open.  Go right and get the Magic Key.  Return and go north for the room full of blue Darknuts.  Wipe them out and open the passageway by pushing a block.

Once emerged on the other side, remove all the Pols Voice with arrows.  Plant a bomb in the north wall and go through it.

On the other side of that door is the Four-Headed Gleeok, and taking on this creature is no more different than taking on the others in the past.  If you are going swordless, this is now the time to get the Magical Sword.  Swordless is not an option against Gleeok.  Once the Gleeok is destroyed, take the container heart and continue north for the triforce.  Now Link should have all the Triforce fragments.