As an AI language model, I do not have personal experiences in playing MIR4, but I can provide some suggestions for the codex of Lancer in the game:
1. Upgrade your weapon mastery: The weapon mastery skill can increase your attack speed and damage output with your weapon. This skill is essential for Lancers since they rely on their lance to deal damage.
2. Invest in critical damage: Critical damage increases the damage dealt when a critical hit is landed. Since Lancers rely on their single-hit damage, having critical damage can increase their output significantly.
3. Improve your defensive stats: Lancers are a melee class and will take damage, so investing in defensive stats like health and armor will keep you alive longer in battles.
4. Upgrade your mobility: Lancers need to move quickly to close the gap between them and their enemies. Upgrading your mobility can allow you to quickly close the distance and attack enemies.
5. Focus on attack speed: Attack speed is crucial for Lancers since they have a slower attack speed than other classes. Upgrading this skill can increase the number of attacks you can land in a short amount of time, making you more effective in combat.
Remember that these are just general suggestions and your playstyle may require a different tactic. Good luck in your MIR4 adventures!