Whenever you cast a noncopy spell, this creature gets +X/+0 until end of turn, where X is the base mana cost of that spell.
I Have Erratic Cyclop in play and Cast “Hazoret’s Undying Fury” aka HUF
HUF Resolve , and Cyclop get +21/+0
4 “Approach of the Second Sun” aka ASS shows up and have cost reduce to 0
When ASS cast Cyclop get +0/+0
It Seems Cyclop doesn’t see the Base Casting Coss of ASS (16).
Ah but this is correct 
HUF unfortunately modifies the base mana cost of a spell (if you will look at it, it doesn’t have its cost in ‘green’ as a reduced cost, or ‘red’ as an increased cost).
Means of reducing costs without affecting the base mana cost seem to be Immortal Sun & Electromancer for spells, Convoke, Ghalta and other similar specific reduction cards (of their own) etc.
The descriptions are the problem here 
We see this in other areas, right, like how Teferi can use his first to bounce Ghalta when Ghalta’s reduced cost is in effect.
Except teferi A1 doesn’t word as “Base Mana cost”
Hi, can we get an update on this? Because this definitely looks like a bug, i.e. behavior not as intended. How can “base mana cost” be called that, if there are effects that can modify it? “Base mana cost” should be just that, i.e. cost as originally shown on the card, that doesn’t get modified even if the card is cast for a reduced or raised cost.