I was asking my local judge and he wasn't certain about the interaction of blood sun and lands like gruul turf, sheltered thicket and copperline gorge when it came to their enter the play tapped clauses. He was thinking they entered play untapped as if blood sun was treating them like blood moon. but we didn't have time to double check to be exact.
will they enter tapped or untapped under blood sun?
The thing making them enter tapped is a replacement effect which is an ability of the card. Since the land no longer has that ability due to Blood Sun, there is nothing making it enter tapped.
Blood Sun's effect, just like Blood Moon's, takes away certain abilities, but in a different way (with Blood Sun, this happens just by making all lands lose most kinds of abilities, but with Blood Moon, this happens by making nonbasic lands Mountains and no other land types [compare C.R. 613.1f with C.R. 613.1d and 305.7, respectively]). Both effects take away from the affected lands abilities that make them enter the battlefield tapped, so they work the same way in this scenario:
Since Ixalan, both effects "already exist and would apply to" Gruul Turf, etc., so they are "tak[en] into account" when "determin[ing] whether [those lands'] replacement effects apply and how they apply" (C.R. 614.12, 614.1d). That means that Gruul Turf would enter the battlefield without the abilities in question, so would enter the battlefield untapped since nothing else states otherwise (C.R. 110.5b).
Before Ixalan, both effects would be ignored for the purposes of C.R. 614.12 (as was in effect in Commander 2017). This means that the replacement effects of Gruul Turf, etc., would still work and could make those lands enter the battlefield tapped in the given cases.
EDIT (Mar. 23; Oct. 11): Correctness edit.
EDIT (Jul. 9, 2019): One rule was renumbered with Core Set 2020.
EDIT (Jan. 15, 2020): Correctness edit.
EDIT (Oct. 19, 2021): Edited slightly.
I was asking my local judge and he wasn't certain about the interaction of blood sun and lands like gruul turf, sheltered thicket and copperline gorge when it came to their enter the play tapped clauses. He was thinking they entered play untapped as if blood sun was treating them like blood moon. but we didn't have time to double check to be exact.
will they enter tapped or untapped under blood sun?
EDIT (Mar. 23; Oct. 11): Correctness edit.
EDIT (Jul. 9, 2019): One rule was renumbered with Core Set 2020.
EDIT (Jan. 15, 2020): Correctness edit.
EDIT (Oct. 19, 2021): Edited slightly.