“Serial Spell” must be chained to the activation of your Normal Spell Card. Nothing can be chained in-between by yourself or your opponent. If your opponent chains to your Normal Spell Card, you cannot chain “Serial Spell” to that Normal Spell Card. Because of this, it is impossible to chain 2 copies of “Serial Spell” to the same Normal Spell Card.
“Serial Spell” does not target a card.
If you chain “Serial Spell” to a Normal Spell Card that targets a card(s) you can select a different target(s) for the “Serial Spell” copy of the Normal Spell Card.
Discarding your hand is a cost to activate “Serial Spell”. You cannot activate “Serial Spell” if it is the only card in your hand, or if it is Set and you have no cards in your hand.
“Serial Spell” only copies the effects of your Normal Spell Card, not any costs of that Spell Card. So if you chain “Serial Spell” to “Delinquent Duo” you do not pay an additional 1000 Life Points.
If you activate “Monster Reborn”, and chain “Serial Spell”, discarding your entire hand, you can select and revive one of the monsters you discarded for the cost of “Serial Spell” to be the monster that “Serial Spell” Special Summons to the field. (For example, if you target “Dark Magician” with “Monster Reborn”, then chain “Serial Spell” and discard “Buster Blader”, you can use “Serial Spell” to Special Summon the “Buster Blader” you discarded to activate “Serial Spell”.)
You cannot level up “Horus the Black Flame Dragon” from 4 to 8 with just “Level Up!” and “Serial Spell”. Because you would send “LV4” to the Graveyard for “Level Up!”, but even if you copy it with “Serial Spell”, the first “Level Up!” hasn’t resolved, so “LV6” isn’t on the field to send to the Graveyard as a cost for the copy of “Level Up!” If you have “Horus the Black Flame Dragon LV4” and “Armed Dragon LV3” on the field, and send one of them to the Graveyard with “Level Up!”, you cannot use “Serial Spell” to Level Up the other monster, since there was no monster sent to the Graveyard as a cost for “Serial Spell”, and “Serial Spell” would have no point of reference to resolve its effect.
If you chain “Serial Spell” to “Swords of Revealing Light” it will copy the effect of flipping all monsters face-up, but it will not remain on the field and prevent the opponent from attacking. This is because it is a Quick-Play Spell Card and is sent to the Graveyard after the chain resolves.
If you chain “Serial Spell” to “Different Dimension Capsule” it will copy the effect and remove 1 card you select in your Deck from play, face-down. But because “Serial Spell” does not remain on the field, the selected card remains removed from play face-down and is not placed in your hand.
You can activate “Serial Spell” to copy the effect of a Normal Spell Card, even if it is “Raigeki” or “Soul Exchange” and copying the effect serves no real purpose.
If you have 2 monsters in your Graveyard, and your opponent only has 1 monster in their Graveyard, you can activate “The Shallow Grave” and chain “Serial Spell”, even though you would not normally be able to activate a second “The Shallow Grave” because your monster would no longer have any monsters in the Graveyard. As a result, you will Special Summon 2 monsters and your opponent will only Special Summon 1 monster.
If you chain “Serial Spell” to “Bait Doll”, the entire effect of “Bait Doll” is applied and “Serial Spell” is also shuffled back into your Deck.
If you chain “Serial Spell” to “Dragged Down into the Grave”, the player who activated “Serial Spell” has no cards in hand, so the effect of “Dragged Down into the Grave” is impossible to resolve, and the effect disappears.
If you chain “Serial Spell” to “Metamorphosis”, there is no effect because you did not Tribute a monster for a cost, so “Serial Spell” has no point of reference and cannot resolve.
If you chain “Serial Spell” to “Monster Gate” resolve the effect of “Monster Gate” twice (once for “Serial Spell” and once for “Monster Gate”) even though you only pay the cost once (for “Monster Gate”).