It is an excellent card for farming LDs but a very situational card for PvP.
You need to have Temple of the Kings on the field to use the card.
Serket is mostly used in decks to get high score against Legendary Duelists. Here are cards usually used with Serket to achieve "Over 9,999 Damage" or "Over 5,000 Damage" with "Effect Damage Only" if possible.
high attack monsters that are difficult to summon , but can be special summoned using Serket and Temple of the Kings. They can be used as part of the Gravekeeper's Vassal Combo, dealing 9999+ damage in one attack.
Once you successfully special summon BEUD or OZ, use 2 copies of Union Attack to increase the ATK of this monster card. If you finish the duel using Vassal and deal over 9,999 damage without dealing any battle damage, you are guaranteed to get at least 4000 pts (3000 pts for "over 9,999 damage + 1000 pts for "effect damage only")
Pirahna Army Combo is an alternative to the Gravekeeper's Vassal Combo. Using Gift of the Martyr boost the attack of Piranha Army equal to the attack of the tributed monster. Then attack directly with Piranha Army, which doubles the damage, to deal 9999+ damage. Use Riryoku before Gift of the Martyr if in need of more attack power.