If you cast Dragonshift using overload, only creatures you control when it resolves will be affected. Creatures that come under your control later in the turn will not.

Each affected creature will lose any abilities it may have gained prior to Dragonshift resolving. Notably, this includes the ability to cast the copies of a card with cipher that's encoded on the creature, although that ability will return after the turn ends.

Effects that modify the power or toughness of an affected creature, such as the effects of Phytoburst or Legion's Initiative, will apply to it no matter when they started to take effect. The same is true for counters that change the creature's power or toughness (such as +1/+1 counters) and effects that switch its power and toughness.

Each affected creature will lose all other colors and creature types and be only red, blue, and a Dragon. Each will retain any other types it may have had, such as artifact.

If any of the affected creatures gains an ability after Dragonshift resolves, it will keep that ability.

Dragonshift overwrites all previous effects that set a creature's power or toughness to specific values. However, effects that set a creature's power or toughness to specific values that start to apply after Dragonshift resolves will overwrite this effect.

If you are instructed to cast a spell with overload "without paying its mana cost," you can't choose to pay its overload cost instead.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as an overload cost), add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.

If you don't pay the overload cost of a spell with overload, that spell will have a single target. If you pay the overload cost, the spell won't have any targets.

Because a spell with overload doesn't target when its overload cost is paid, it may affect permanents with hexproof or with protection from the appropriate color.