Player Beth has a 4/4 double strike creature.
Player Carl has a 4/4 creature that can block Beth's creature
Combat starts and Beth attacks with her creature. Carl blocks with his creature.
First strike damage is dealt. Carl's creature dies without dealing damage back.
Normal combat damage step: Does Beth's creature deal damage to Carl now, or does Beth need a trample effect on her creature to do that? I ask, because I think you can do instant-speed combat effects between first strike combat damage and normal combat damage.
The attacking creature remains blocked even if no creatures are blocking it anymore; since the attacking creature doesn't have trample, it assigns no combat damage (C.R. 509.1h, 510.1c; compare with C.R. 702.19d).
In any case, players will get priority to cast instant spells after creatures, if any, assign and deal combat damage during any combat damage step (whether a normal one or one created because of double strike or otherwise) (C.R. 510.3, 702.4b, 116.1a). All double strike does is give a combat phase two combat damage steps rather than one (and restrict which creatures assign combat damage during those steps) (C.R. 702.4b). Double strike doesn't mean—
that a creature with that ability assigns twice its power in combat damage (see also this thread), or
that that creature assigns and deals combat damage, then assigns and deals combat damage again, with nothing in between.
So, players have priority after first strike damage is dealt?
If so, if Beth somehow granted trample to her creature before normal combat damage is dealt, would 4 damage be deal to Carl the during normal combat damage step?
Whenever equipped creature deals combat damage, you may put an Aura card from your hand onto the battlefield attached to it."
So, after first strike damage, its triggered ability happens, and if Beth puts Rancor on her creature, will her creature deal 4 damage to Carl during the normal combat step?
Yes, players get priority after combat damage is dealt (even during the first combat damage step).
In this scenario, when Rancor is attached to the attacking creature due to Holy Avenger, it will still be the first combat damage step (the game won't move on to the second combat damage step yet). Alternatively, Beth could cast a spell such as Seedling Charm to give the attacking creature trample.
Player Carl has a 4/4 creature that can block Beth's creature
Combat starts and Beth attacks with her creature. Carl blocks with his creature.
First strike damage is dealt. Carl's creature dies without dealing damage back.
Normal combat damage step: Does Beth's creature deal damage to Carl now, or does Beth need a trample effect on her creature to do that? I ask, because I think you can do instant-speed combat effects between first strike combat damage and normal combat damage.
In any case, players will get priority to cast instant spells after creatures, if any, assign and deal combat damage during any combat damage step (whether a normal one or one created because of double strike or otherwise) (C.R. 510.3, 702.4b, 116.1a). All double strike does is give a combat phase two combat damage steps rather than one (and restrict which creatures assign combat damage during those steps) (C.R. 702.4b). Double strike doesn't mean—
See also these threads:
If so, if Beth somehow granted trample to her creature before normal combat damage is dealt, would 4 damage be deal to Carl the during normal combat damage step?
Specifically, the new card Holy Avenger reads:
"Equipped creature has double strike.
Whenever equipped creature deals combat damage, you may put an Aura card from your hand onto the battlefield attached to it."
So, after first strike damage, its triggered ability happens, and if Beth puts Rancor on her creature, will her creature deal 4 damage to Carl during the normal combat step?
In this scenario, when Rancor is attached to the attacking creature due to Holy Avenger, it will still be the first combat damage step (the game won't move on to the second combat damage step yet). Alternatively, Beth could cast a spell such as Seedling Charm to give the attacking creature trample.