If all of the spell's targets are illegal when the spell tries to resolve, it won't resolve and none of its effects will happen.

A card with a splice ability can't be spliced onto itself because the spell is on the stack (and not in your hand) when you reveal the cards you want to splice onto it.

You reveal all cards you intend to splice at the same time. Each individual card can be spliced only once onto any one spell.

You choose all targets for the spell after revealing cards you want to splice, including any targets required by the text of any of those cards. You may choose a different target for each instance of the word "target" on the resulting spell.

Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature may become lethal if you switch its power and toughness during that turn.

Switching a creature's power and toughness twice (or any even number of times) effectively returns the creature to the power and toughness it had before any switches.

Effects that switch a creature's power and toughness apply after all other effects, regardless of when those effects began to apply. For instance, if you target a 1/2 creature then give it +2/+0 later in the turn, it's a 2/3 creature, not a 4/1 creature.