# Rideable Tank: Introduction and Interactions

## Abstract:

Combined arms gameplay with the M432A Longstreet Tank was once a core part of CM-SS13. Unfortunately, the implementation of multitile vehicles is one that makes it a slog both for marines to fight alongside such vehicles and for xeno players to fight them. At the root of this issue is the fact that multi-tile vehicles are handled as dense objects that act like mobile walls. They block firing lines, they prevent xenos from pushing, and they occupy a lot of space that could otherwise be used by marines to maneuver around the front. This project seeks to remedy those issues by introducing mechanics that allow marines and xenos to ride and move atop the tank, and interact with the environment and others as they do so. While this clears up space for marines and adds to their firepower, this also makes them more vulnerable to specific xeno castes and strains such as the boiler and oppressor praetorian.

## Goals:

1) Generally improve upon the experience of playing alongside with the tank: Reduce instances of body-blocking. Allow easier movement around the tank. Lessen the physical impact that a 3x3 vehicle has on the space of the front.

2) Open up new alternatives for Xeno players to exploit the use of the tank in their favor. Marines riding atop the tank open themselves to being more vulnerable to many Xenomorph abilities.

3) Shed light on the possibility of re-adding the tank as a mainstay of CMSS13, making it non mutually-exclusive with the ARC or VTOL as they all serve different purposes.

## Non-Goals:

1) Make the tank a marine powerhouse / New SPEC. The goal is to keep the tank in a fire-support role. It should be a valuable tool for marines, but it should be incapable of skirmishing up to the Queen and acting as a second, un-stunnable SADAR spec, which used to be a problem with LTB.

2) Nullify the movement burden the tank has on the front. The tank should still hinder marine movement slightly: Retreating with the tank behind will be slower as marines have to climb up the hull. Advancing will be slower as the tank might potentially block marines.

3) Touch armor, weapons and modules balance. While this is something that can be done in subsequent PRs, the scope of this project is restricted to movement changes.

4) Invalidate the purpose of the ARC or the upcoming V-TOL.

# Body:

Marines and all xeno castes are now able to climb atop the tank. If the tank moves or turns, their position gets updated accordingly. Climbing up and down the tank incurs a small delay.

Entities atop the tank do not get burnt from tiles on fire. Marines also do not trigger acid and hugger traps, but eggs will still open and facehug humans on top. Boiler resin traps also do not slow down marines, but acid mines still work perfectly.

Projectile interaction has also been tweaked: The tank still stops bullets, but you can hit entities ontop it by sprite-clicking them. This works both for marine weapons and for xeno abilities, including but not limited to acid spits, Boiler's acid shotgun, Prae hooks, pounces, so on and so forth. You still can not hit entities on the opposite side of the tank if you are not on top of it.

Xenos that have pounce abilities (Rav, Runner, Lurker, etc...) can pounce atop the tank to climb it with no delay.

Xenos can damage the tank from above, while riding it, incurring a 30% penalty to damage and the inability to hit the threads. Tank crewmen have to either get out to deal with the threat or ensure they are close to marines who can peel Xenomorphs off of them.

With high enough speeds, marines atop the tank will be jousted and stunned after a crash.

## Alternatives:

1) APC. Those same changes could also be retroactively applied to the APC and other multi-tile vehicles. I feel, however, that the APC is more of a generalist vehicle and might be more difficult to balance, while the tank remains exclusively in a fire-support role.

## Potential Changes:

1) Climbing up-and-down times: Currently, everyone takes 1.5 seconds to climb up or down the tank. This value either makes the tank's presence negligible, or makes it no better than the 3x3 barricade it used to be. Requires careful adjusting.

2) Stuns: Being forcibly removed from atop the tank stacks a 3 second Weaken on top of you if you are a human. This might be a bit too punishing.

3) Jousting: Currently, when a tank crashes into something at sufficient speed, all mobs (e.g Marines, Xenos, Queen, King...) atop it get a small Weaken, plus a 3 sec stun if they aren't a xeno and get knocked off the tank. This might require balancing or the blacklisting of certain mob_sizes.

## Future ideas:

1) More tools for Xenos to counter the tank. In particular, the Trapper Boiler's resin traps could slow it down, or act like roadblocks. Gas traps could be triggered only by multi-tile vehicle movement and be balanced around it.

2) Repairs. As is, once a module gets destroyed, it's gone forever. Allowing hardpoints to be fixed with valuable materials such as Plasteel could ensure that the tank can be recoevered and repaired after a counter-push, while still not being a disposable tool.

3) Resin structure interactions: Resin spikes should do some damage to the treads, sticky resin could make the tank more sluggish, et-cetera.

4) All movable atoms could hop atop the tank. Currently this is limited to mobs, but it is possible to make it so items and deployables can be brought atop the tank: From simply dropping your gun ontop it, to pulling marines in rollerbeds atop, placing down ammo boxes, and maybe even deploying barricades, turrets or Mortar.

5) Expand this behavior to be part of vehicle/multitile instead of just multitile/tank. Transform math will need refactoring for vehicles that aren't 3x3, but it is entirely possible to add this behavior to all vehicles.

# TO-DO:

1) PR & Address balance issues

2) Make ARC and TANK non-mutually exclusive

3) Adjust player pop cap for TANK to be available