Use this card's last effect to target a monster like "Marshmallon" or "Obnoxious Celtic Guard", ensuring that this monster doesn't get destroyed by battle (which it likely will, if you had to activate this card's effect in the first place).
If this card is targeted for an attack by a non-DARK monster, target "Ally of Justice Catastor" so the opponent's monster will be destroyed before damage is calculated.
Another option would be to use "Blackwing - Jin the Rain Shadow" for a Synchro Summon (such as Catastor) and later target him with this monster's effect. It will destroy any monster with 2800 or fewer DEF without calculating damage. In certain situations this is more beneficial than using Catastor (such as against a DARK monster).
Alternately, one can also target "The Wicked Avatar" to absolutely ensure that Hermos's ATK will be higher than his opponent's (unless Hermos's opponent is "The Wicked Avatar").
Keep in mind that this card's name becomes the targeted monster's name until your next End Phase. It doesn't just acquire its ability. You can use this to your advantage by using cards that require specific monsters to be in Play such as "Photon Stream of Destruction". However, since you cannot target a Normal Monster you cannot use cards like "Burst Stream of Destruction".
If one of your other Legendary Knights was destroyed previously you can select them and use its effect to set a card from your Graveyard.
If you are able to protect this card during the turn it is attacked you can target a "Black Luster Soldier - Envoy of the Beginning" in your Graveyard to be able to use either its Banishing effect to get rid of a problematic monster your opponent has or even get two attacks off.
Since this card becomes the name of the targeted monster you are unable to summon out "Timaeus the Knight of Destiny" during your turn if you use this cards effect. However, since it remains a Warrior-Type you can activate "Legend of Heart" and use it as the tribute and bring it back with its normal name.