Tainted Grail: Conquest

This is an achievement that you can make much, much easier for yourself, by keeping a small deck. Once you go above the 15 card mark, unless you have lots of Tomes of Knowledge, you will never be drawing it all in one turn with only 3 energy. With the right setup, you should be able to both draw and play every card in the same turn, which will net you the more difficult achievement.

The easiest faction to do this with when set up correctly are the Watchers of Tuathan. The Zealot, Sentinel and Apostate will each start with the same 14 card deck, 4 of which are zero cost Shot cards. Of these, choose the Zealot. If you are following my solutions for "I Don't Need Much","Zealot" or "I Have the Power", you will be aiming for the same 8 card deck. The cards you want to remove are Quiver Cards, Bow Draw, Stepping Stones, Smoke Shot and one or more standard Shot cards.

The opportunities for removing cards are few and far between, so even if they will put you in a bit of a dicey spot, take the opportunity when you can. To my knowledge, the ways you can remove cards are:

Witch - Sacrifice 80% current max HP and remove up to 5 cards
Elderly Archer - Remove 2 cards at no detriment if his quest has been completed. Otherwise costs 10HP (I think)
Hunting Grounds - Instead of choosing to hunt, rest and fight the monsters that come, then choose to remove up to 2 cards.
Master-at-Arms - The Master-at-Arms villager can remove 1 (by default) card per run for 100 Wealth, can gain another if has the upgrade costing 400 Card Shreds (1 gained per card not taken when opportunity arises)

Assumig that you are able to reach the 8 card deck, you should have Shot x3, Feints x4 and Aimed Shot. 5 cards are already drawn for you, so you will need way to draw the reamaining 3. This will be Tomes of Knowledge. By default, they draw one additional card, so you would need to collect 3 of them in a run, which is not impossible (as they are sold by some shops and the Scientist) but not simple either. If you upgrade them at the Scientist, they can draw more cards per use. However, what is much more likely is that you will have some Calc Runestones. These allow you to draw extra cards on the first turn, 1 per upgrade level. If you have a Flawless Calc, you will automatically draw your entire deck of 8 when you enter a battle. However, this requires a lot of luck with Runestone drops, it is much more likely to only have a Polished. This will draw 2 of the extra cards for you, so you need only 1 unupgraded Tome of Knowledge to draw the last card