: Halo needs a sticking C4. One that goes beyond the Sticky Grenande. One that
: is basically what the beta tripmine was. Sneaking into an enemy base,
: placing it on one of their warthogs, and then sneaking away were some of
: my most favorable moments.

I'd imagine if 343 ever did this, they would want it to function in both the campaign and in competitive sandboxes (as probably an additional grenade type), since they're pretty gung-ho about continuity. The problem with campaign is that you're never really doing much of any Splinter Cell type maneuvers or sabotaging the enemy before actually opening fire.

However, I can picture a few campaign use cases some anything-goes players would use it in:
* Special delivery: plant it on a ghost and charge the enemy. You jump out and hide behind some cover once close by, letting say a grunt or a really stupid elite go "oh shit, a ghost, I'ma taking this". They get in, and bam, EXPLOSIONS?
* Making lemon-aid: plant it on a friendly's vehicle (that you're not riding in of course), so as soon as they scoot by, say a wraith, it blows them all up.
* Great journey or bust: When the player dies (in campaign), the explosive self activates, causing any cocky grunts or elites who get up close to shoot their dead bodies to get a nice little proximity surprise (that you can witness while in the death cam, right before the checkpoint is reloaded)

Or they could 'combat evolve' the plasma grenade so that it has multiple firing modes. The first being the usual, stick and arm for a few seconds. The other being a stick and arm for proximity. Depending on how it was implemented, it'd may be the least invasive way (continuity and gameplay wise) to implement this (as a grenade anyway).