Surging Sentinels

First strike is a static ability that modifies the rules for the combat damage step. (See rule 510, “Combat Damage Step.”)

If at least one attacking or blocking creature has first strike or double strike (see rule 702.4) as the combat damage step begins, the only creatures that assign combat damage in that step are those with first strike or double strike. After that step, instead of proceeding to the end of combat step, the phase gets a second combat damage step. The only creatures that assign combat damage in that step are the remaining attackers and blockers that had neither first strike nor double strike as the first combat damage step began, as well as the remaining attackers and blockers that currently have double strike. After that step, the phase proceeds to the end of combat step.

Giving first strike to a creature without it after combat damage has already been dealt in the first combat damage step won’t preclude that creature from assigning combat damage in the second combat damage step. Removing first strike from a creature after it has already dealt combat damage in the first combat damage step won’t allow it to also assign combat damage in the second combat damage step (unless the creature has double strike).

Multiple instances of first strike on the same creature are redundant.

Ripple is a triggered ability that functions only while the card with ripple is on the stack. “Ripple N” means “When you cast this spell, you may reveal the top N cards of your library, or, if there are fewer than N cards in your library, you may reveal all the cards in your library. If you reveal cards from your library this way, you may cast any of those cards with the same name as this spell without paying their mana costs, then put all revealed cards not cast this way on the bottom of your library in any order.”

If a spell has multiple instances of ripple, each triggers separately.