The Good:
Can bypass healers, by stacking incredible damage.
High knockdown rate on charge (especially against effective enemies).
Picking up an attack orb before detonation is greatly effective.
Incredible charge time makes charge spamming easy (hitting enemies is a different story).
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The Bad:
Slow bullets require up close combat for full effectiveness and countering enemy reaction time.
Tags have relatively low damage requiring a dozen or so tags to take down a large target.
Mechanic can be confusing to new players.
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The Ugly:
Hard to use in parties with players who don't understand or respect your purpose with the catalyzer. By attacking your target and killing it before you detonate it, this effectively wastes your time and theirs as you can handle that large enemy while they could be tackling the smaller ones.
Using this gun long range on targets that excel at dodging (devilites, thwackers, menders, wolvers) is difficult.
Bullets orbit outside the target essentially halving tag damage to targets with shields.
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Worse:
Can't deal low damage. This is problematic when finishing off low health mobs. You simply cant without spamming another 500+ damage.