The Four Aces would be an upgrade that allows the user to get one of four benefits every round. The benefits are noticeable, but also carry a drawback and are chosen at random, though they do not repeat themselves - if the user gets the Ace of Diamonds, then the next round they'll get any other Ace than the Ace of Diamonds.
[Ace of Diamonds]
The Ace of Diamonds would give the user's Main Gun a large increase in damage (chosen randomly between +30-+60) but would give them a matching reduction to fire rate. When the Ace of Diamonds is being used, the user bullets leave a blue trace.
[Ace of Hearts]
The Ace of Hearts would give the user a large increase in maximum hp (chosen randomly between +50%-+100%), but would completely negate any healing upgrade they have. In the case of Regeneration, the user would take damage instead of recovering HP. When the Ace of Hearts is in effect, the user leaves a faint red trail when moving.
[Ace of Spades]
This Ace would give the user a large increase in knife range and attack speed, chosen randomly between +40%-+80% and +25%-+50% respectively. In turn, however, the user will be unable to use any directly offensive skill, this includes the main gun, grenades, and main gun attachments. In case the user has Throwing Knife, range affects the flight speed of the knife as well. When in effect, the user of Ace of Spades radiates a faint black aura, with a gray spade tail on their back.
[Ace of Clovers]
The Ace of Clovers would give the user a large increase in critical chance, of +30%-+60%, and would give them a small chance (of 5-10%) to gain a chosen upgrade twice at the end of the round. If the upgrade is at max tier or has only 1 tier, the Ace of Clovers will instead double it's given critical hit chance. In the case the user's critical chance goes above 100, critical hits have a chance to deal more even more damage. However, the user will have between 45-90% reduced HP. When in use, the user leaves green patches on the ground.