Notes & Combos
My preferred endboard: Lancea, Gymir Aegerine, and Spellbreaker.
This summons you 2 floodgates on the opponents turn, protects you from destruction or banishment, and keeps opponents off of spells. Gymir Aegerine makes for a more protective endboard. Evenly matched is still dangerous however. If you want to play around that, you can go for Dragite.
Select notes on cards:
Mirror Mage general search priority: Georgious --> Winds --> other depending on situation
If it wasn't UR, I would play old Brionac over new Brionac. Old Brio can get rid of multiple cards, and the discard can be partially bypassed by Revealer.
Hexa - its effect to lower opponents' attack is quite useful at times, so your opponent doesn’t just attack over your floodgates which are around the 2k mark.
Georgious - floodgate ability that is good going first and second (against flamberge/ishizu/spirit of yubel for example).
Winds - A lot of people don’t make the most of this card, but if I have some kind of access to getting mirror mage on the field for its token generating effect, this is my go-to search off of mirror mage’s gy effect. This card can get you exactly the cards you need for specific onboard pieces. I often use it in the mirror mage combo where there will be a level 5 mirror mage and 3 tokens. I tribute 2 of the tokens to get spell breaker and revealer/speaker if I already have revealer in gy. This will get me to a level 10 synchro (with a draw through coral dragon) and a spellbreaker which stops your opponent from activating spells. Good card if you get interrupted and you can just get free bodies from the deck to continue playing. Gy effect is also good for recovery on the crackback.
Spellbreaker - Often special summon this off of winds. Can be a complete turn ender by not letting the opponent use a spell. Usually also bypass the discard through revealers gy effect.
Also, just as a tip: don't always prioritize the draw 4 combo. I see a lot of players do that, including in Youtube videos, but that, in my experience, is too reliant upon the draws and non-engine. It's better to go for a guaranteed stronger boss monsters unless the situation requires that you draw.
Under Maxx C going first, I try to end on a Lancea in as few summons, if possible. The deck can steal wins under Shifter. You just have to play without Mirror Mage's gy effect or discard Mirror Mage before the opponent shifters.
If you have any questions, please let me know. Hope this helps!